The shape of a piece of land is a trapezoid with a height of 30 meters. If the bottom is reduced by 18 meters, the shape of the land becomes a square. What is the area of the original trapezoid?
一块地的形状是梯形，高30米，如果下底减少18米，这块地的形状就变成了正方形，原来梯形的面积多少？
<gadget id="calculator">30 + 18 + 30</gadget>
<output>78</output>

<gadget id="calculator">30 / 2</gadget>
<output>15</output>

<gadget id="calculator">78 * 15</gadget>
<output>1_170</output>

<result>1_170</result>