[tex]64=4\cdot4\cdot4=4^3\\\\\left(\dfrac{1}{4}\right)^{c-2}=64\\\\\left(\dfrac{1}{4}\right)^{c-2}=4^3\\\\\left(\dfrac{1}{4}\right)^{c-2}=\left(\dfrac{1}{4}\right)^{-3}\iff c-2=-3\ \ \ |+2\\\\\boxed{c=-1}\\\\\text{check}\\\\L_s=\left(\dfrac{1}{4}\right)^{-1-2}=\left(\dfrac{1}{4}\right)^{-3}=4^3=64=R_s\\\\\text{correct :)}[/tex]
[tex]\text{Used:}\\\\a^{-n}=\left(\dfrac{1}{a}\right)^n[/tex]
