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This is in the form (a+b)^n where a = 3x, b = -2y and n=6.

n=(n0)xn+(n1)xn−1y+⋯+(nn−1)xyn−1+(nn)yn=∑k=0n(nk)xn−kyk

x + y) n = (n 0) x n + (n 1) x n - 1 y + \dots + (n n - 1) x y n

=(6X5X4)/(3X2X1)(3x)^3(-2y)^3

= (-20)(27x^3)(8y^3)

= -4320 x^3y^3

Therefore the coefficient of 4th term is 4320