Hello from MrBillDoesMath!
Answer:
Take you pick below! (either x 8 or x = 7.01, approx, depending how the question is interpreted)
Discussion:
Interpretation 1
If the question is 2^(x -1) = 128, then as 2^7 = 128,
x-1 = 7 so x = 8
Interpretation 2
If the question is (2^x -1) = 128, then..
2^x = 128 + 1 = 129 =>
log(2^x) = log(129) =>
xlog(2) = log(129) =>
x = log (129) / log2 = 7.01
Regards,
MrB