A trapezoid has an area of 45 square meters, a height of 5 meters, and an upper base of 7 meters. What is its lower base?
一块梯形的地面积为45平方米，高是5米，上底是7米，求它的下底是多少？
<gadget id="calculator">5 / 2</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">7 * (5/2)</gadget>
<output>35/2 = around 17.5</output>

<gadget id="calculator">45 - (35/2)</gadget>
<output>55/2 = around 27.5</output>

<gadget id="calculator">(55/2) / (5/2)</gadget>
<output>11</output>

<result>11</result>