The ISS has been described as the most expensive single item ever constructed. In 2010 the cost was expected to be $150 billion. This includes NASAs budget of $58.7 billion (inflation-unadjusted) for the station from 1985 to 2015 ($72.4 billion in 2010 dollars), Russias $12 billion, Europes $5 billion, Japans $5 billion, Canadas $2 billion, and the cost of 36 shuttle flights to build the station; estimated at $1.4 billion each, or $50.4 billion in total. Assuming 20,000 person-days of use from 2000 to 2015 by two- to six-person crews, each person-day would cost $7.5 million, less than half the inflation-adjusted $19.6 million ($5.5 million before inflation) per person-day of Skylab.
Question: How many years was the time span of NASAs $58.7 billion budget for the cost of the ISS station?
Answer: 30