Answer:
30 mph
Step-by-step explanation:
let s represent speed and h represent rebound.
Given that s is proportional to h then the equation relating them is
s = kh ← k is the constant of proportion
To find k use the condition s = 20, h = 10, then
20 = 10k ( divide both sides by 10 )
2 = k
s = 2h ← equation of proportionality
When h = 15 , then
s = 2 × 15 = 30 mph