There are two ropes, the length of which is three times the length of the short rope, and if 20 meters are subtracted from each of the two ropes, the length of the rope is exactly four times the length of the short rope. How long is the long rope in meters?
有两条绳子，长的是短的3倍，如果从这两根绳子上各减去20米，长的就正好是短的4倍．长绳原来长多少米．
<gadget id="calculator">3 - 1</gadget>
<output>2</output>

<gadget id="calculator">4 - 3</gadget>
<output>1</output>

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

<gadget id="calculator">20 * 2</gadget>
<output>40</output>

<gadget id="calculator">40 + 20</gadget>
<output>60</output>

<gadget id="calculator">60 * 3</gadget>
<output>180</output>

<result>180</result>