A rectangular vegetable field is 90 meters long and 40 meters wide. If the width is increased by 5 meters, how many meters must the length be reduced to keep the area constant?
一块长方形菜地长90米，宽40米．如果宽增加5米，要使面积不变，那么长应该减少多少米？
<gadget id="calculator">40 + 5</gadget>
<output>45</output>

<gadget id="calculator">40 / 45</gadget>
<output>8/9 = around 0.888889</output>

<gadget id="calculator">90 * (8/9)</gadget>
<output>80</output>

<gadget id="calculator">90 - 80</gadget>
<output>10</output>

<result>10</result>