piece of wood is a meter long. After a section is used up, the remaining part is exactly (1/3) more than what was used up. Find the number of meters used up.
一截木材长a米，用去一段后，余下的正好比用去的多(1/3)，求用去了多少米．
<gadget id="calculator">3 / 7</gadget>
<output>3/7 = around 0.428571</output>

<result>3/7 = around 0.428571</result>