During the flood fighting and rescue battle, after the soldiers smashed a 7-meter-long wooden pile into the river, (1/5) of it was above the water, and (2/7) was in the soil at the bottom of the river. How deep is the river?
抗洪抢险战斗中，战士将一根7米长的木桩砸入河水中后，其中(1/5)露出水面，(2/7)在河底的泥土中，河水深多少米？
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">1 - (1/5) - (2/7)</gadget>
<output>18/35 = around 0.514286</output>

<gadget id="calculator">7 * (18/35)</gadget>
<output>18/5 = around 3.6</output>

<result>18/5 = around 3.6</result>