Help please? Don’t know what to do?

Witch represents the inverse of the function f(x)=1/4x-12

Asales representative from a local radio station is trying to convince the owner of a small fitness club to advertise on her station. the representative says that if the owner begins advertising on the station today, the club's total number of members will grow exponentially each month. she uses the given expression to model the number of club members, in hundreds, after advertising for t months.

What is the length of the midsegment of a trapezoid with bases of length 15 and 25 ?