The upper base of a trapezoid is 5.8 cm, the lower base is 9.4 cm, and the height is 4 cm. What is its area?
一个梯形的上底是5.8厘米，下底是9.4厘米，高4厘米，它的面积是多少．
<gadget id="calculator">5.8 + 9.4</gadget>
<output>15.2</output>

<gadget id="calculator">4 / 2</gadget>
<output>2</output>

<gadget id="calculator">15.2 * 2</gadget>
<output>30.4</output>

<result>30.4</result>