The sum of the upper and lower bases of a trapezoid is 30 cm, and the height of the trapezoid is 6 cm. What is the area of the trapezoid in square centimeters?
一个梯形的上底与下底的和是30厘米，梯形的高是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">30 * 3</gadget>
<output>90</output>

<result>90</result>