Rob and Amy each improved their yards by planting rose bushes and shrubs. They bought their supplies from the same store. Rob spent $100 on 8 rose bushes and 5 shrubs. Amy spent $112 on 8 rose bushes and 8 shrubs. What is the cost of one rose bush and the cost of one shrub?

shrub: $4 rose bush: $10

Step-by-step explanation:

Amy bought 3 more shrubs than Rob, and paid $12 more. Thus, each shrub must cost $12/3 = $4.

Rob's 5 shrubs cost him $4*5 = $20, so the $80 remainder of his $100 total cost paid for 8 rose bushes. Then the cost of one rose bush is ...

... $80/8 = $10