7. (i) Evaluate the integral D (6xy + 3y?) dady , where (a) D is the square 0

7. (i) Evaluate the integral (6xy + 3y2)dxdy where (a) D is the square 0 3,0 y 2; (b) D is the triangle with vertices (0, 0), (1, 1) and (2, 0) .