First, you have to realize that 2^-2 = 1/2^2. Therefore 2^(x-2) = 2^x/2^2. So:

2^x(1-1/2^2)=3(2^13) factor 2^x from the first term

John, those two parts make absolutely no sense to me. Could you please explain how you got 2^(x-2)=2^x/2^2? I'm completely lost. Thanks