The area of a trapezoid is 30 square centimeters. If its upper and lower bases remain the same and its height is tripled, what is its area?
一个梯形的面积是30平方厘米，如果它的上底和下底不变，高扩大到原来的3倍，则它的面积是多少．
<gadget id="calculator">30 * 3</gadget>
<output>90</output>

<result>90</result>