The quadrilateral has two parallel sides, so meets the definition of a trapezoid. The diagram shows its base lengths (the lengths of the parallel sides) to be 4 and 8, and the distance between those bases (the height) to be 6. The appropriate formula for the area (A) is
... A = (1/2)(b₁ + b₂)·h
Fill in the numbers and do the arithmetic.
... A = (1/2)(4 + 8)·6
... A = (1/2)·12·6
... A = 6·6 = 36
The area of the trapezoid is 36 square units.