project is completed in 10 days by teams A and B, and by team A in 15 days alone. After 4 days of cooperation, team A will do the rest alone. How many days will it take to complete?
一项工程，甲、乙两队合做10天完成，甲队独做15天完成，两队合作4天后，剩下的由甲队独做，还需要几天完成？
<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">(1/10) * 4</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (2/5)</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">(3/5) / (1/15)</gadget>
<output>9</output>

<result>9</result>