Let f be a differentiable function such that $f^{\prime }\left(x\right)=7-\frac{3}{4}\frac{f\left(x\right)}{x},\left(x>0\right)$ and $f\left(1\right)\ne 4.$ then $\underset{x\to 0^{+}}{\lim }xf\left(\frac{1}{x}\right):$