Question

How many hours did she pay to have the bike checked out

Answer 1

An equation like $8x+15=The Final Price$ would work cause it's 15 plus 8 times the hours used. 

If you paid 63 then you would have $8x+15=63$

Solve it by first subtracting 15 over and having 
$8x=48$
Divide both sides by 8 and finally get 

$x=6$

Answer 2

15 + (8 x h)

63 -15 = 48

48 / 8 = 6

Joan rented the bike for 6 hours.