A trapezoidal field, the upper base is 50 meters, the lower base is 20 meters longer than the upper base, and the height is as long as the lower base. What is the area of the land in square meters?
一块梯形田地，上底50米，下底比上底长20米，高和下底同样长，这块地的面积是多少平方米？
<gadget id="calculator">50 + 20</gadget>
<output>70</output>

<gadget id="calculator">50 + 70</gadget>
<output>120</output>

<gadget id="calculator">70 / 2</gadget>
<output>35</output>

<gadget id="calculator">120 * 35</gadget>
<output>4_200</output>

<result>4_200</result>