The number of square units is what called "area" . The area of a trapezoid can be computed as : [tex]A=\dfrac{(b+B)\times h}{2}[/tex] where b is the length of the short basis, B is the length of the long basis and h is the Height. If you place the vertices of the trapezoid, you'll notice that b=2, B=6 and H=4. Is it clear to you ?
