The sum of the upper and lower bases of a trapezoid is 15 cm and the height is 6 cm. What is the area of the trapezoid in square centimeters?
一个梯形上底与下底的和是15厘米，高是6厘米，这个梯形的面积是多少平方厘米．
<gadget id="calculator">6 / 2</gadget>
<output>3</output>

<gadget id="calculator">15 * 3</gadget>
<output>45</output>

<result>45</result>