Well c is the cost to rent the locker for 1 hour, the 1.5 is the rental time, so multiplied together, you get the 9 which is the total cost to rent the locker for the number of hours you had it for.
for example: if you were to rent the locker for 1 hour (t = 1) the equation would look like c(1) = total cost.
*hopefully this is making sense*
another example: if you wanted to find out what the base rate is to rent the locker for 1 hour, you would just solve for c in the given equation
