The outer exponent is 4 so there will be 5 terms all together. By rules of exponents
C(4,0)(3^4)(2^0)(x^8)(y^0) + C(4,1)(3^3)(2^1)(x^6)(y^3) + C(4,2)(3^2)(2^2)(x^4)(y^6) + C(4,3)(3^1)(2^3)(x^2)(y^9) + C(4,4)(3^0)(2^4)(x^0)(y^12)
The coefficient of the 3rd term: C(4,2)(3^2)(2^2) = 6 x 9 x 4 = 216