A rectangular vegetable field is 20 meters long and its width is less than its length (7/10). What is the area of this vegetable field?
一块长方形菜地长20米宽比长少(7/10)．这块菜地的面积是多少？
<gadget id="calculator">7 / 10</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">1 - (7/10)</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">20 * (3/10) * 20</gadget>
<output>120</output>

<result>120</result>