Answer
$-125t^{12}$
Work Step by Step
When we raise a term inside parentheses to a power, we must raise each factor to that power, and then multiply. To raise a power to a power, we multiply the exponents. Therefore, $$(-5t^4)^3=(-5)^3(t^4)^3=-125t^{4\times 3}=-125t^{12}$$
