Use the binomial theorem and match the power of y to decide the value of k. Once k is known, the power of x is automatically n-k. The general term is C(6,k)(3x)^(6-k)(2y)^k. For k=5, the coefficient is C(6,5)·3^1·2^5=576. Remember that the numerical coefficient comes from the binomial coefficient and the constants attached to x and y, including any negative sign.