(5^2)^-3/5^-8

(5^2)^-3/5^-8    so we have

(5²)^-3/ 5^-8   and by a law of exponents, we can write

5^-6 / 5^-8      and again, by an exponent law, we have

5⁸ / 5⁶ = 5^8-6 = 5² =  25