This task involves creating questions from a given passage that involve some kind of complex reasoning (including numerical reasoning).
The generated questions must require looking at more than one part of the passage to answer. Try to use a variety of reasoning types in your questions (some of the sample reasoning types are illustrated in the 'positive examples' field) and also have a variety of answer types (spans, numbers, dates). A span is a continuous phrase taken directly from the passage or question. In such questions, the answer spans are recommended to be five words. Questions with answer type "number", are expected to start with "How many". For instance, "How long did an event last?" can be phrased as "How many years did an event last?". To increase diversity, try to create more questions for which the answer will be multiple spans. Please create questions that require AT LEAST 2 arithmetic operations as illustrated in the 'positive examples' field. You are encouraged to try DIFFERENT COMBINATIONS of operations and not just limit to the combinations shown in those examples. The more challenging questions you create, the better it is.

Passage: Charleston is a popular tourist destination, with a considerable number of hotels, inns, and bed and breakfasts, numerous restaurants featuring Lowcountry cuisine and shops. Charleston is also a notable art destination, named a top-25 arts destination by AmericanStyle magazine. Commercial shipping is important to the economy. The city has two shipping terminals, owned and operated by the South Carolina Ports Authority, which are part of the fourth-largest container seaport on the East Coast and the thirteenth-largest container seaport in North America. Charleston is becoming a popular location for information technology jobs and corporations, and this sector has had the highest rate of growth between 2011 and 2012, due in large part to the Charleston Digital Corridor. In 2013, the Milken Institute ranked the Charleston region as the ninth-best performing economy in the US because of its growing IT sector. Notable companies include Blackbaud, SPARC, BoomTown, CSS, and Benefitfocus. In June 2017, the mean sales price for a home in Charleston was $351,186 and the median price was $260,000.
How many IT companies is Charleston known for?