$f\left(\frac{x^2-5x}{2x-7}\right)=\frac{7-2x}{2x^2-10x}-4$
$f\left(\frac{x^2-5x}{2x-7}\right)=\frac{-(2x-7)}{2(x^2-5x)}-4$
$f\left(\frac{x^2-5x}{2x-7}\right)=\frac{-1}{\frac{2(x^2-5x)}{2x-7}}-4\rightarrow f(x)=\frac{-1}{2x}-4$olur.
$f(4^{x+1})=\frac{-1}{2.4^{x+1}}-4=3-4^{x-1}$
$-2^{-2x-3}-4=3-2^{2x-2}\Rightarrow x=log_4(14+\sqrt{786}) $