To repair a section of railway, replace the original 9-meter-long old rails with new 12-meter-long rails. How many new rails need to be replaced with the original 84 old rails on this section of railway?
修一段铁路，要用每根12米长的新铁轨换下原来每根长9米的旧铁轨．这段铁路原有84根旧铁轨需要换多少根新铁轨？
<gadget id="calculator">9 / 12</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">84 * (3/4)</gadget>
<output>63</output>

<result>63</result>