'A' and 'B' together can do a piece of work in 12 days while 'B' and 'C' together can do the same work in 20 days. 'A' started the work alone and worked on it for 2 days, then 'B' alone worked on it for 16 days and 'C' alone completed the remaining work in 18 days. Find the time taken by 'B' alone to complete the whole work.