A project can be completed by A alone in 20 days and by B in 30 days. Now two people are working together, A rests for 3 days, B rests for a day, and it takes 16 days from start to finish, a=how many days.
一项工程，甲独做20天完成，乙独做30天完成．现在两人合做，其中甲休息了3天，乙休息了a天，开始到完工用了16天，a=多少天．
<result>5.5</result>