A triangular meadow, the length of the base is 20m, and the height is 4m less than the base, find the area of the meadow.
一块三角形草地，底边长20m，高比底少4m，求草地的面积．
<gadget id="calculator">20 - 4</gadget>
<output>16</output>

<gadget id="calculator">16 / 2</gadget>
<output>8</output>

<gadget id="calculator">20 * 8</gadget>
<output>160</output>

<result>160</result>