‘A’ is twice as efficient as ‘B’, and ‘B’ is half as efficient as ‘C’. ‘A’ and ‘B’ start working together, but after 4 days, ‘B’ leaves and ‘C’ joins ‘A’. Together, ‘A’ and ‘C’ complete the remaining work in 5 more days. Find the time taken by ‘C’ alone to complete the whole work.