Question: What is the western border of the continent that has 3 countries who use the rand rather than their own legal tender?

Context paragraphs:
Europa coin programme: The Europa Coin Programme, also known as the European Silver Programme, or the Eurostar Programme, is an initiative dedicated to the issuance of collector-oriented legal tender coins in precious metals to celebrate European identity.  The issuing authorities of EU member countries voluntarily contribute coins to the Europa Coin Programme.  Multiple countries have participated in the programme, beginning in 2004.  Some coins are denominated in euro, others are denominated in other currencies.  Europa coins are legal tender.

Niue dollar: Niue, a country in free association with New Zealand, uses two official legal tender currencies.  While they use the New Zealand dollar, the government also issues legal tender coins using the Niue dollar for collector's purposes.

Non-circulating legal tender: Non-circulating legal tender (NCLT) refers to coins that are theoretically legal tender and could circulate but do not because their issue price, and/or their melt value at the time of issue is significantly above the arbitrary legal tender value placed thereon.  They are sold to collectors and investors with no intention that they be used as money.  Notable examples would include commemoratives, proofs, bullion coins, presentation sets, patterns and the like.

Legal tender: Legal tender is a medium of payment recognized by a legal system to be valid for meeting a financial obligation.  Paper currency and coins are common forms of legal tender in many countries.  Legal tender is variously defined in different jurisdictions. Formally, it is anything which when offered in payment extinguishes the debt.  Thus, personal cheques, credit cards, and similar non-cash methods of payment are not usually legal tender.  The law does not relieve the debt obligation until payment is tendered.  Coins and banknotes are usually defined as legal tender.  Some jurisdictions may forbid or restrict payment made other than by legal tender.  For example, such a law might outlaw the use of foreign coins and bank notes or require a license to perform financial transactions in a foreign currency.

United States Note: A United States Note, also known as a Legal Tender Note, is a type of paper money that was issued from 1862 to 1971 in the U.S. Having been current for more than 100 years, they were issued for longer than any other form of U.S. paper money.  They were known popularly as "greenbacks", a name inherited from the earlier greenbacks, the Demand Notes, that they replaced during 1862.  Often termed Legal Tender Notes, they were named United States Notes by the First Legal Tender Act, which authorized them as a form of fiat currency.  During the 1860s the so-called "second obligation" on the reverse of the notes stated:

Namibia: Namibia ( , ), officially the Republic of Namibia (German:    ; Afrikaans: "Republiek van Namibië" ) is a country in southern Africa whose western border is the Atlantic Ocean.  It shares land borders with Zambia and Angola to the north, Botswana to the east and South Africa to the south and east.  Although it does not border Zimbabwe, a part of less than 200 metres of the Zambezi River (essentially a small bulge in Botswana to achieve a Botswana/Zambia micro-border) separates the two countries.  Namibia gained independence from South Africa on 21 March 1990, following the Namibian War of Independence.  Its capital and largest city is Windhoek, and it is a member state of the United Nations (UN), the Southern African Development Community (SADC), the African Union (AU), and the Commonwealth of Nations.

United Precious Metals Association: The United Precious Metals Association is a Utah-based non-profit dedicated to offering its members gold and/or silver denominated accounts.  UPMA was founded shortly after the passage of the Utah Legal Tender Act in 2011.  This Act explicitly recognizes the circulation of U.S minted legal tender gold and silver coins as a non-taxable event.  Only Utah has legal tender laws on the books.

Legal Tender Cases: The Legal Tender Cases were a series of United States Supreme Court cases in the latter part of the nineteenth century that affirmed the constitutionality of paper money.  In the 1869 case of "Hepburn v. Griswold", the Court had held that declaring paper notes to be legal tender in payment of debts existing prior to the Legal Tender Act of 1862 violated the United States Constitution.  In the "Legal Tender Cases", the Court overruled "Hepburn", beginning with "Knox v. Lee" and "Parker v. Davis" in 1871, and then "Juilliard v. Greenman" in 1884.

South African rand: The South African rand (sign: R; code: ZAR) is the currency of South Africa.  The rand is subdivided into 100 cents (sign: "c").  The ISO 4217 code is ZAR, from Dutch "Zuid-Afrikaanse Rand" (South African rand).  The rand is legal tender in the Common Monetary Area between South Africa, Swaziland, Lesotho, and Namibia, although the latter three countries do have their own currencies.

Lesotho loti: The Loti (plural: Maloti) is the currency of the Kingdom of Lesotho.  It is subdivided into 100 "Lisente" (sg.  "Sente").  It is pegged to the South African rand on a 1:1 basis through the Common Monetary Area, and both are accepted as legal tender within Lesotho.  The loti was first issued in 1966, albeit as a non-circulating currency.  In 1980, Lesotho issued its first coins denominated in both loti and lisente (dated 1979) to replace the South African Rand, but the Rand remains legal tender.

Supporting paragraphs: South African rand Namibia
Answer: Atlantic Ocean