Respuesta :

easy

remember
if x^a=x^b whre x=x, then assume a=b
also
(x^m)^n=x^(mn)
so

(5^n)^3=5^(3n)

now we gots
5^(3n)=5^12
5=5 so assume 3n=12

3n=12
divide by 3 both sides
n=4

a cheat way would be to just evaluate it since you got the options