Use a rope to measure the depth of the well. Fold the rope in three to measure the remaining 16dm outside the well. Fold the rope in four to measure the remaining 4dm outside the well. What is the length of the rope in dm?
用绳子测井深，把绳子三折来量，井外余16dm，把绳子四折来量，井外余4dm，则绳子长多少dm．
<gadget id="calculator">16 - 4</gadget>
<output>12</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(1/3) - (1/4)</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">12 / (1/12)</gadget>
<output>144</output>

<result>144</result>