In a quadrilateral, product of area of diagonally opposite triangles is same.
So, the product of other set of opposite triangles will be 12*27
Now, we have to find minimum a and b such that a*b=12*27 and a+b is minimum.
So a = b = 18 (as 12*27 = 324)
Hence the area of the quadrilateral = 18 + 18 + 12 + 27 = 75