A trapezoid has an average height of 20 cm and a base of 30 cm. What is the area of this trapezoid in square centimeters?
一个梯形，上下底的平均值是30厘米，高是20厘米．这个梯形的面积多少平方厘米．
<gadget id="calculator">20 / 2</gadget>
<output>10</output>

<gadget id="calculator">30 * 2 * 10</gadget>
<output>600</output>

<result>600</result>