If the sum of the upper and lower bases of a trapezoid is 45 cm and the height is 12 cm, what is the area in square centimeters?
一个梯形的上、下底的和是45厘米，高是12厘米，面积是多少平方厘米．
<gadget id="calculator">12 / 2</gadget>
<output>6</output>

<gadget id="calculator">45 * 6</gadget>
<output>270</output>

<result>270</result>