Answer:
9 years
the tree doubles in height
we can make a model
1 x 2 = 2
2 x 2 = 4
4 x 2 = 8
8 x 2 = 16
16 x 2 = 32
32 x 2 = 64
64 x 2 = 128
128 x 2 = 256
256 x 2 = 512
512 x 2 = 1024
Let's say 1024 is the maximum height
half the maximum height is 1024 x 0.5 = 512 so it will take 9 years because it reached 512 on the 9th year
Explanation: