A colored ribbon, half of it was used up for the first time, and the remaining half was used up for the second time, leaving 9 meters left. How long is this ribbon originally?
一条彩带，第一次用去一半，第二次又用去剩下的一半，还剩9米．这条彩带原来长多少米．
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 - (1/2)</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(1/2) * (1/2)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">9 / (1/4)</gadget>
<output>36</output>

<result>36</result>