A project is expected to be completed by 15 people for 4 hours a day and can be completed in 18 days. Later, 3 people are added and the working time is increased by 1 hour. How many days will the project be completed?
一项工程预计15人每天做4小时，18天可以完成，后来增加3人，并且工作时间增加1小时，这项工程多少天完成．
<gadget id="calculator">15 + 3</gadget>
<output>18</output>

<gadget id="calculator">4 + 1</gadget>
<output>5</output>

<gadget id="calculator">18 * 5</gadget>
<output>90</output>

<gadget id="calculator">18 / 90</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">15 * 4 * (1/5)</gadget>
<output>12</output>

<result>12</result>