A rectangular vegetable field is 20 meters long, and its width is 1/4 of its length. Find the area of the rectangular vegetable field.
一块长方形菜地，长20米，宽比长短(1/4)，求长方形菜地的面积．
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">20 * (1/4)</gadget>
<output>5</output>

<gadget id="calculator">20 - 5</gadget>
<output>15</output>

<gadget id="calculator">15 * 20</gadget>
<output>300</output>

<result>300</result>