For this case, what we should do is write an equation of the potential type:
y = A * (b) ^ x
Where,
A: initial height
b: decrease rate of initial height
x: number of bounces.
We have then:
y = 3.5 * (0.75) ^ x
For the ninth bounce:
y = 3.5 * (0.75) ^ x
y = 0.26
Answer:
The height of the 9th bounce of the ball is:
y = 0.26 feet.