A section of railway was undergoing safety inspection, and 15 kilometers were inspected and repaired in the first week, leaving 25% of the total length unrepaired. How long is this railway in kilometers?
一段铁路进行安全检修，第一周检修了15千米，还剩下全长的25%没检修．这条铁路全长多少千米？
<gadget id="calculator">25 / 100</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 - (1/4)</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">15 / (3/4)</gadget>
<output>20</output>

<result>20</result>