When you find the area, you want to break it up into different parts. Therefore, one part would be a square and the other part can be a trapezoid. Start out with finding the area of a square by multiplying 6 and 6. This will get you 36. Then, subtract 6 from 21. This will get you, 15. Then use the area of a trapezoid formula, which is A=(a+b)/2 times H. The H is the heigh, the a and b are the top and bottom bases. So if you plug it into the equation, (7+15)/2 then multiply that by 6 ( which is the height). this will get you 66. If you add 66+36, it equals 102 which is the area