How would I simplify (-5a^3)^4 using the power rule. I have no clue wher to begin if I guesse I would say 20a^3. But I know I am wrong I just need help getting started, thank you.

OK if its like you wrote it, the ^3 only goes to the a not to (-5a)
and the ^4 goes to -5 and the ^3
which makes it:

(-5 * a*a*a)^4

-5^4 * (a*a*a)^4

20 * a^12


you were almost right, you just forgot to take (a^3)^4 as well