The second question has not been fully taken;

There are two methods. The first method is based on 6, and 10 is the height of the shadow area, so the area is 30.

In the second method, you extend the line of 6 to make a parallel line of 10, and you can get a rectangle. The shadow area is the larger triangle minus the smaller triangle, that is, 0.5 (10x20-(20-6) x10) = 30.