distribute what is outside to each part inside. add exponents when multiplying

4y^2 * y^4 = 4*y*y * y*y*y*y = 4y^6

4y^2 * -9y^3 = (4*-9)*y*y*y*y*y = -36y^5

4y^2 * 6y = (4*6)*y*y*y = 24y^3

4y^2 * 2 = 8y^2

So the final answer is 4y^6-36y^5+24y^3+8y^2