that's easy u might b knwin d curves of y^2=x andx^2=y
des curves r of similar type ......so first drw them then find d point of intersection of d curves
u get y =(4)*(a^2*b)^1/3
ohk ..........nw 
integral frm 0 to (4)*(a^2*b)^1/3
solvin u get d answer as 16ab/3 sq units