It has been 4 days to build a 500-meter-long water canal, and 120 meters are repaired every day. How many meters are left to be repaired?
修一条长500米的水渠，已经修了4天，每天修120米，还剩多少米没有修？
<gadget id="calculator">120 * 4</gadget>
<output>480</output>

<gadget id="calculator">500 - 480</gadget>
<output>20</output>

<result>20</result>