The upper base of a trapezoid is 4 cm, the lower base is 8 cm, and the height is 7 cm. What is the area of the trapezoid in square centimeters?
一个梯形的上底是4厘米，下底是8厘米，高是7厘米，这个梯形的面积是多少平方厘米．
<gadget id="calculator">4 + 8</gadget>
<output>12</output>

<gadget id="calculator">7 / 2</gadget>
<output>7/2 = around 3.5</output>

<gadget id="calculator">12 * (7/2)</gadget>
<output>42</output>

<result>42</result>