Question 122612
Let x= hours that the car has been parked so:

for example you have to pay 4+2,5(2) for 3 hours then in gral

you have to pay 4 +2,5(x-1)for x hours 

so you have to resolve 4 +2,5(x-1)> 16,5 so 2,5(x-1)>12,5 so 2,5x>15 so x>6

R:The car has been parked for more than 6 hours