For a project, team A works for 2 days and team B works for 5 days, and the total project is completed (4/15); if team A works for 5 days, and team B works for 2 days, the total project is completed (19/60) , how many days does B need to complete the task alone?
一项工程，甲队做2天，乙队做5天，一共完成全部工程的(4/15)；若甲队做5天，乙队做2天，一共完成全部工程的(19/60)，乙单独完成任务需要多少天？
<result>30</result>