So, if the pizza guy earns $7.50 an hour & $2 per delivery, every delivery price is going to be found with 7.50h + 2d (p). The driver spends $114 on his car a week ($28 + $86). Since the driver works 40 hours a week and you need to know how many deliveries are needed to earn $300, the equation will now be p - 114 = 300.
We now know h = 40, so p is now 300 + 2d.
(300 + 2d) - 114 = 300
2d - 114 = 0
2d = 114
d = 57
