A trapezoid has an upper base of 80 cm, a lower base of 100 cm, and a height of 50 cm. What is the area of this trapezoid.
一个梯形的上底是80厘米，下底是100厘米，高是50厘米．这个梯形的面积是多少．
<gadget id="calculator">80 + 100</gadget>
<output>180</output>

<gadget id="calculator">50 / 2</gadget>
<output>25</output>

<gadget id="calculator">180 * 25</gadget>
<output>4_500</output>

<result>4_500</result>