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(12,k)(2x)^(12-k)(y)^k. For k=1, the coefficient is C(12,1)·2^11·1^1=24576. Remember that the numerical coefficient comes from the binomial coefficient and the constants attached to x and y, including any negative sign.