What is the coefficient of the x9y-term in the binomial expansion of (2y + 4x3)4?

To get x^9, choose the 4x^3 term three times, since 3 × 3 = 9. The remaining factor is 2y, giving the y-term. The coefficient is (4 choose 3) × 4^3 × 2 = 4 × 64 × 2 = 512, so the coefficient is 512.

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