The key thing here is that x is the number of years AFTER 1990, therefore for part A plug in 0 to get 743 For part B plug in 12 and 17 then subtract the smaller from larger. I got 1470.6 for 2007 and 1380.2 for 2002 Subtracting gives 90.4, which rounds to 90 because .4 of a prisoner doesn't make sense