12 people work together to complete a project in 15 days. Now it needs to be completed 3 days ahead of schedule. How many more people are needed? (Solve with ratio)
12个人合做一项工程，15天完成，现在要提前3天完成，需要增加几人？(用比例解)
<gadget id="calculator">12 * 3</gadget>
<output>36</output>

<gadget id="calculator">15 * 12</gadget>
<output>180</output>

<gadget id="calculator">12 * 15</gadget>
<output>180</output>

<gadget id="calculator">180 - 180</gadget>
<output>0</output>

<gadget id="calculator">36 + 0</gadget>
<output>36</output>

<gadget id="calculator">15 - 3</gadget>
<output>12</output>

<gadget id="calculator">36 / 12</gadget>
<output>3</output>

<result>3</result>