A rope, used 30%, used exactly 15m. How many meters is this rope?
一根绳子，用了30%，正好用了15m．这很绳子有多少米？
<gadget id="calculator">30 / 100</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">15 / (3/10)</gadget>
<output>50</output>

<result>50</result>