The depth of the well is 20 meters, which is exactly equal to 5 times the difference between the waterless part of the well minus the water depth part. What is the water depth in meters?
井深20米，正好等于井的无水部分减去水深部分差的5倍，水深多少米．
<gadget id="calculator">20 * 5</gadget>
<output>100</output>

<gadget id="calculator">100 - 20</gadget>
<output>80</output>

<gadget id="calculator">5 + 5</gadget>
<output>10</output>

<gadget id="calculator">80 / 10</gadget>
<output>8</output>

<result>8</result>