The below figure consists of a rectangle and the numbers labeled over the top represents the area of that particular shaded region.

Calculate the area of the green region labeled as '?'

The White triangle is similar to the Red triangle

As ratio of areas = ratio of bases when height is same,

Ratio of sides is 2:3

White triangle = 9/4 * Red triangle = 9/2

Thus the Green Region = 5.5 units.