For a project, it is estimated that 30 people can complete the task in 15 days. After working for 4 days, another 3 people were added. How many days in advance can the task be completed if everyone is working at the same rate?
一项工程，预计30人15天可以完成任务．后来工作4天后，又增加3人．如果每人的工作效率相同，这样可以提前几天完成任务？
<gadget id="calculator">30 * 15</gadget>
<output>450</output>

<gadget id="calculator">30 * 4</gadget>
<output>120</output>

<gadget id="calculator">450 - 120</gadget>
<output>330</output>

<gadget id="calculator">30 + 3</gadget>
<output>33</output>

<gadget id="calculator">330 / 33</gadget>
<output>10</output>

<gadget id="calculator">10 + 4</gadget>
<output>14</output>

<gadget id="calculator">15 - 14</gadget>
<output>1</output>

<result>1</result>