Let \( f:\mathbb{R}\to\mathbb{R} \) satisfies \( f(x+y)=2^{x}f(y)+4^{y}f(x),\ \forall x,y\in\mathbb{R}. \) If \( f(2)=3 \), then \( 14\cdot \frac{f'(4)}{f'(2)} \) is equal to ______.