Let the tree grow by a constant amt 'k'
Height at end of 4th yr = 4+ 4k
Height at end of 6th yr = 4+ 6k
since at the end of 6th year, the tree was 1/5 taller than it was at end of 4th yr,
(4+6k) - (4+4k) = 1/5 (4+4k)
2k=1/5(4+4k)
10k=4+4k
6k=4
k=2/3
Hence tree grew by a rate of 2/3 every yr.
OA?