For two ropes of the same length, the first one takes 30 meters, the second one takes 18 meters, and the remaining second one is 3 times as long as the first one. How many meters is each rope?
同样长的两根绳子，第一条用去30米，第二条用去18米，剩下的第二条是第一条的3倍．原来每条绳子长多少米？
<gadget id="calculator">30 * 3</gadget>
<output>90</output>

<gadget id="calculator">90 - 18</gadget>
<output>72</output>

<gadget id="calculator">3 - 1</gadget>
<output>2</output>

<gadget id="calculator">72 / 2</gadget>
<output>36</output>

<result>36</result>