For a certain task, if teams A and B work together, their respective work efficiency can be increased to 1.2 times the original. After 15 days of cooperation between the two teams, it will take 9 days for the remaining tasks to be completed by team A alone. It takes 7 days to complete. How many days will it take for group B to complete the task alone?
某项任务，如果甲、乙两个小组合作，各自的工作效率能提高到原来的1.2倍，两个小组合作15天后，剩下的任务由甲小组单独完成需9天，那么由乙小组单独完成需7天．那么由乙小组单独完成整项任务需多少天．
<gadget id="calculator">1.2 * 15</gadget>
<output>18</output>

<gadget id="calculator">7 / 9</gadget>
<output>7/9 = around 0.777778</output>

<gadget id="calculator">1.2 * 15 * (7/9)</gadget>
<output>14</output>

<gadget id="calculator">18 + 14 + 7</gadget>
<output>39</output>

<result>39</result>