The bottom of a triangle is 10 centimeters, and its area is 80 square centimeters. How many centimeters should the bottom be shortened to reduce its area by 20 square centimeters?

The bottom of a triangle is 10 centimeters, and its area is 80 square centimeters. How many centimeters should the bottom be shortened to reduce its area by 20 square centimeters?

20÷80=1/4
10 × 1 / 4 = 2.5cm
A: the bottom edge should be shortened by 2.5cm