Explanation:
remember, when multiplying the same base with different exponents, we add the exponents.
when putting exponents to the power of exponents, we multiply the exponents (as simplified shortcut of all the additions we would actually have to do).
((-3)²)⁴ = (-3)⁸
in "slow motion" :
((-3)²)⁴ = (-3)²×(-3)²×(-3)²×(-3)² = (-3)^(2+2+2+2) = (-3)⁸
(-3)² = 9
9⁴ = 6561
(-3)⁸ = 6561