There is a trapezoidal wheat field, the lower base is 280m, which is twice the upper base, and the height is 50m. What is the area of the trapezoid in m**2.
有一个梯形麦田，下底280m，是上底的2倍，高是50m，梯形的面积是多少m**2．
<gadget id="calculator">280 / 2</gadget>
<output>140</output>

<gadget id="calculator">280 + 140</gadget>
<output>420</output>

<gadget id="calculator">50 / 2</gadget>
<output>25</output>

<gadget id="calculator">420 * 25</gadget>
<output>10_500</output>

<result>10_500</result>