I'm assuming you meant to say "it reaches a height that is 2/3 the height of the previous bounce".
We have a geometric sequence with a = 9 as the first term and r = 2/3 as the common ratio.
The nth term is a*(r)^(n-1) = 9*(2/3)^(n-1)
Set this equal to 3 and solve for n. You'll need logs to isolate the exponent.
9*(2/3)^(n-1) = 3
(2/3)^(n-1) = 3/9
(2/3)^(n-1) = 1/3
log[ (2/3)^(n-1) ] = log(1/3)
(n-1)*log(2/3) = log(1/3)
(n-1)*(-0.17609) = -0.47712
n-1 = (-0.47712)/(-0.17609)
n-1 = 2.7095235
n = 2.7095235+1
n = 3.7095235
Unfortunately we don't get a whole number. We can see that the terms of the sequence are:
9, 6, 4, 2.667
Each term is found by multiplying 2/3 by the previous term.
We don't land exactly on "3". The closest we get is 2.667 approximately.
So to answer the question, there is no way to get to exactly 3 feet above the ground based on a whole number of bounces.