The upper base of the trapezoid is 18 cm, the lower base is 22 cm, and the height is 15 cm. What is the area in square centimeters?
梯形的上底是18厘米，下底是22厘米，高是15厘米，面积是多少平方厘米．
<gadget id="calculator">18 + 22</gadget>
<output>40</output>

<gadget id="calculator">15 / 2</gadget>
<output>15/2 = around 7.5</output>

<gadget id="calculator">40 * (15/2)</gadget>
<output>300</output>

<result>300</result>