To build a road with a length of 4.5km, 0.3km is repaired every day. After 7 days of repairing, if the remaining 0.4km is repaired every day, how many days will it take?
修一条长4.5km的路，每天修0.3km，修了7天后，剩下的如果每天修0.4km，还要修多少天？
<gadget id="calculator">0.3 * 7</gadget>
<output>2.1</output>

<gadget id="calculator">4.5 - 2.1</gadget>
<output>2.4</output>

<gadget id="calculator">2.4 / 0.4</gadget>
<output>6</output>

<result>6</result>