WHAT IS X/10 /6/8/9X IT IS HARD SO HERE

What is the average rate of change for this function for the interval from x=2 to x=4 ?

The tuition costs, c, for a local community college are modeled by c(h) = 250 + 200h, where h represents the number of credit hours taken. the local state university has tuition costs, s, modeled by the function s(h) = 300 + 180h. how many credit hours will a student have to take for the two tuition costs to be equal? round the answer to the nearest tenth of an hour.

If f(x)=3x+1 and f^-1=x-1/3, then f^-1(7)=