Answer
$$-4t^{11}+8t^9+20t^8$$
Work Step by Step
We multiply these expressions out using the distributive property, ensuring that every value multiplied by a given set of parenthesis is multiplied by everything inside of the parenthesis. Doing this, we find:
$$ \left(-4t^8\right)t^3+\left(-4t^8\right)\left(-2t\right)+\left(-4t^8\right)\left(-5\right)\\ -4t^8t^3+4\cdot \:2t^8t+4\cdot \:5t^8\\ -4t^{11}+8t^9+20t^8$$