A rope is used up (1/4), and there are 3 meters left, what is the original length of this rope in meters?
一根绳子用去(1/4)，还剩3米，这根绳子的原长是多少米．
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 - (1/4)</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">3 / (3/4)</gadget>
<output>4</output>

<result>4</result>