Question: McCarrs Creek, New South Wales is at the headwaters of a semi–mature tide located about how far  north of the Sydney central business district

Context paragraphs:
Campbelltown, New South Wales: Campbelltown is a suburb and major centre in the metropolitan area of Sydney, New South Wales, Australia.  It is located in Greater Western Sydney 50 km south-west of the Sydney central business district.  Campbelltown is the administrative seat of the local government area of the City of Campbelltown.  It is also acknowledged on the register of the Geographical Names Board of New South Wales as one of only four cities within the Sydney metropolitan area.

McCarrs Creek, New South Wales: McCarrs Creek is a suburb that is located adjacent to McCarrs Creek, approximately 4 km west of Newport, at the headwaters of the Pittwater in northern Sydney, in the state of New South Wales, Australia.  McCarrs Creek was gazetted as a suburb on 20 January 2012.

Port Hacking: Port Hacking (Aboriginal Tharawal language: Deeban), an open youthful tide dominated, drowned valley estuary, is located in southern Sydney, New South Wales, Australia approximately 30 km south of Sydney central business district.  Port Hacking has its source in the upper reaches of the Hacking River south of Helensburgh, and several smaller creeks, including South West Arm, Bundeena Creek and The Basin and flows generally to the east before reaching its mouth, the Tasman Sea, south of Cronulla and north–east of Bundeena.  Its tidal effect is terminated at the weir at Audley, in the Royal National Park.  The lower estuary features a substantial marine delta, which over time has prograded upstream.  There is also a substaial fluvial (riverine delta) of the Hacking River at Grays Point.  The two deltas are separated by a deep basin.

Pittwater: Pittwater is a semi–mature tide dominated drowned valley estuary, located about 40 km north of the Sydney central business district, New South Wales, Australia; being one of the bodies of water that separate greater Metropolitan Sydney from the Central Coast.

Badgerys Creek, New South Wales: Badgerys Creek, also known as Badgery's Creek, is a suburb of Sydney, in the state of New South Wales, Australia, located approximately 51 km west of the Sydney central business district, in the local government areas of the City of Liverpool.  It is part of the Greater Western Sydney region and is adjacent to the suburbs of Kemps Creek and Austral.

Hawkesbury River: The Hawkesbury River (also Hawkesbury-Nepean River), is a semi–mature tide dominated drowned valley estuary located to the west and north of Sydney, New South Wales, Australia.  The Hawkesbury River and its associated main tributary, the Nepean River, virtually encircle the metropolitan region of Sydney.

Chippendale, New South Wales: Chippendale is a small inner-city suburb of Sydney, New South Wales, Australia on the southern edge of the Sydney central business district, in the local government area of the City of Sydney.  Chippendale is located between Broadway to the north and Cleveland Street to the south, Sydney Central railway station to the east and the University of Sydney to the west.

Middle Harbour: Middle Harbour (or "Warring-Ga"), a semi–mature tide dominated drowned valley estuary, is the northern arm of Port Jackson, an inlet of the Tasman Sea located north of Sydney central business district on the coast of New South Wales, Australia.

Broken Bay: Broken Bay, a semi–mature tide-dominated drowned valley estuary, is a large inlet of the Tasman Sea located about 50 km north of Sydney central business district on the coast of New South Wales, Australia; being one of the bodies of water that separate greater Metropolitan Sydney from the Central Coast.  Broken Bay is the first major bay north of Sydney Harbour.

Tank Stream: Tank Stream, a fresh water tributary of Sydney Cove, located in New South Wales, Australia, was the fresh water supply for the fledgling colony of New South Wales in the late 18th century.  Today it is little more than a storm water drain.  It originated from a swamp to the west of present-day Hyde Park and at high tide entered Sydney Cove at what is now the intersection of Bridge and Pitt Streets in the Sydney central business district.  The catchment was 65 ha , corresponding roughly the size of the Sydney central business district.

Supporting paragraphs: McCarrs Creek, New South Wales Pittwater
Answer: 40 km