Here a, b, c, & d are areas of the triangles.
There are 2 of each letter which means each area has its equal twin.
In other words, every letter is an area of a triangle that shares the same height and base with its twin triangle in terms of area.
Using this knowledge we can use the areas given below to find the area of the shaded region
(b+c) + (a+d) = 16 + 32 = (a+b) + (c+d) = 20 + required area
Required area = 16 + 32 - 20 = 28 cm^2.