Connect the points in the square with the four corners.

Then use triangles with equal bases and equal heights to make the areas equal.

Suppose that the triangle area corresponding to each side is

A, b, c and d

Then there is

A+B= 16？ ①

B+C=20？ ②

C+D=32？ ③

Beg? A+D

It's obvious? ①+③-② Available.

The required area is

16+32-20=28