A trapezoid, the sum of the upper and lower bases is 18cm, and the height is 5cm, what is the area of the trapezoid in cm**2.
一个梯形，上底与下底的和是18cm，高是5cm，这个梯形的面积是多少cm**2．
<gadget id="calculator">5 / 2</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">18 * (5/2)</gadget>
<output>45</output>

<result>45</result>