A 500-meter road has been repaired for 4 days, x meters are repaired every day, how many meters are left to be repaired.
一条500米的公路，已经修了4天，每天修x米，还剩多少米没有修．
<gadget id="calculator">500 - 4</gadget>
<output>496</output>

<result>496</result>