The upper base of a trapezoid is 3 decimeters, the lower base is 7 decimeters, and the height is 5 decimeters. What is its area?
一个梯形的上底是3分米，下底是7分米，高5分米，它的面积是多少？
<gadget id="calculator">3 + 7</gadget>
<output>10</output>

<gadget id="calculator">5 / 2</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">10 * (5/2)</gadget>
<output>25</output>

<result>25</result>