#### Answer

$50$ square centimeters

#### Work Step by Step

RECALL:
The area $A$ of a triangle can be found using the formula $A= \frac{1}{2}bh$ where b = base and h = height.
The given polygon is a triangle with a base of 20 cm and a height of 5 cm.
Use the formula above to obtain:
$A = \frac{1}{2}20(5) = 50$ square centimeters