A piece of wood is half used up for the first time, and the remaining half is used up for the second time, leaving 15 meters left. How long is the piece of wood originally?
一根木条，第一次用去一半，第二次又用去剩下的一半，还剩下15米，这根木条原来长多少米．
<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">15 / (1/4)</gadget>
<output>60</output>

<result>60</result>