Need with 18 and 20 would be appreciated you need to find the variable

When the ball has traveled a distance of

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.

Iknow its nothing to do with education, but what type of thing should i wrote here? ? : ) its for mcdonald's btw.