Find the area of parallelogram given A(2,1), B(7,1), C(9,5) and D(4,5).

MY WORK:

1-I plotted each point on the xy-plane.

2-I determined the base to be 5 and the height to be 8.

3-I then usedA = bhand found the area to be 40.

However, the math book tells me that the area is 20.

How can this be?