f(x) = 2(2)^x-1
The way you wrote, I really don't know it's f(x) = 2(2)^x - 1 or f(x) = 2(2)^(x-1)?
so i'm going to solve both
f(x) = 2(2)^x - 1
f(5) = 2(2)^5 - 1
f(5) = 2(32) - 1
f(5) = 64 - 1
f(5) = 63
f(x) = 2(2)^(x-1)
f(5) = 2(2)^(5-1)
f(5) = 2(2^4)
f(5) = 2(16)
f(5) = 32