What is the area of the shaded part?

The sum of is their base times the height which is 10 for both of the triangles, and then divided by two. We have (BC × 10 + CD × 10) ÷ 2, which equals ( (BC + CD) × 10) ÷ 2. Since we see that BC + CD is 20, we actually have 20 × 10 ÷ 2, which equals 100.