$f(2x-5)=2^{(2x-5)+3}=2^{2x-2}$
$f(x-1)=2^{(x-1)+3}=2^{x+2}$
$\frac {f(2x-5)}{f(x-1)}=\frac {2^{2x-2}}{2^{x+2}}=2^{(2x-2)-(x+2)}=2^{x-4}$
$256=2^{8}$ olduğuna göre
$x-4=8$
$x=12$