There are two ropes. The length of the white rope is 2 meters less than 4 times the length of the red rope. If the length of the white rope is 18 meters, how long is the length of the red rope?
有两根绳子，白绳的长度比红绳的4倍少2米，如果白绳长18米，红绳长多少米．
<gadget id="calculator">18 + 2</gadget>
<output>20</output>

<gadget id="calculator">20 / 4</gadget>
<output>5</output>

<result>5</result>