The area of a trapezoidal test field is 900 square meters, its height is 30 meters, the bottom is 48 meters, how many meters is the top? (solution with equation)
一块梯形试验田的面积是900平方米，它的高是30米，下底是48米，上底是多少米？(用方程解答)
<gadget id="calculator">30 / 2</gadget>
<output>15</output>

<gadget id="calculator">48 * 15</gadget>
<output>720</output>

<gadget id="calculator">900 - 720</gadget>
<output>180</output>

<gadget id="calculator">180 / 15</gadget>
<output>12</output>

<result>12</result>