A canal has been repaired for 300 meters, which is 20 meters shorter than the remaining four times. How many meters are left to be repaired? (Solution of column equation)
一条水渠，已修300米，比剩下的4倍少20米，还剩多少米没有修？(列方程解)
<gadget id="calculator">300 + 20</gadget>
<output>320</output>

<gadget id="calculator">320 / 4</gadget>
<output>80</output>

<result>80</result>