First, find the center, which is base times height or 6 times 3, which is 18. Then, find the triangles(I combine both). Subtract 3 from 6 to get 3. You get a triangle with a base of 3 and a height of 3. Triangle formula = base*height/2. 3*3/2 = 4.5. 18 + 4.5 = 22.5. The area of the trapezoid is 22.5 cm sq.