If f(x)=2xf(x) = 2^xf(x)=2x, which of the following is equal to f(x+3)−f(x)f(x+3) - f(x)f(x+3)−f(x)?
7⋅2x7 \cdot 2^x7⋅2x
8⋅2x8 \cdot 2^x8⋅2x
3⋅2x3 \cdot 2^x3⋅2x
2x+12^{x+1}2x+1