The upper base of a trapezoid is 7 cm, the lower base is twice as large as the upper base, and the height is 3 cm less than the lower base. What is its area in square centimeters?
一个梯形的上底是7厘米，下底是上底的2倍，高比下底少3厘米，它的面积是多少平方厘米．
<gadget id="calculator">7 * 2</gadget>
<output>14</output>

<gadget id="calculator">7 + 14</gadget>
<output>21</output>

<gadget id="calculator">14 - 3</gadget>
<output>11</output>

<gadget id="calculator">11 / 2</gadget>
<output>11/2 = around 5.5</output>

<gadget id="calculator">21 * (11/2)</gadget>
<output>231/2 = around 115.5</output>

<result>231/2 = around 115.5</result>