We can solve it by tree method.
T(n) = T(n/3) + T(n/9) + n
n =======> n
/ \
n/3 n/9 =======> 4/9n
/ \ / \
n/9 n/27 n/27 n/81 ====> $(4/9)^{2}*n$
.................................................................
T(1) ....................................................T(1)
Total work done will be = n + (4/9)n + $(4/9)^{2}*n $ + .........................k (times)
Here n = $(4/9)^{k}$
We can write it like n* [ 1 + 4/9 + 4/9^2 +------------------------]
So, it will be.
= 9/5 *n
= O(n)