Answer:
n = 8.
Explanation:
I am assuming that the sum is 255.
The last term is 128 and the common ratio is 2 so we can work backwards until we reach a sum of 255.
Term n = 128 so the previous term must be 128/2 = 64.
So following this pattern we have:
128 + 64 + 32 + 16 + 8 + 4 + 2 + 1 = 255.
So we see that n = 8.