5,250 rails are needed to lay 5 kilometers of rails. The road construction team needs to lay 20 kilometers of rails. 18,000 rails have already been shipped. How many more rails need to be shipped?
铺5千米的铁轨需要枕朩5250根，筑路队要铺设20千米的铁轨，已经运来枕朩18000根，还需要运来多少根？
<gadget id="calculator">20 / 5</gadget>
<output>4</output>

<gadget id="calculator">4 * 5_250</gadget>
<output>21_000</output>

<gadget id="calculator">21_000 - 18_000</gadget>
<output>3_000</output>

<result>3_000</result>