13.294. Two workers were assigned to manufacture a batch of identical parts; after the first worked for $a$ hours, and the second for $0.6 a$ hours, it turned out that they had completed $5 / n$ of the entire work. After working together for another $0.6 a$ hours, they found that they still had to manufacture $1 / n$ of the entire batch of parts. How many hours will each of them, working separately, need to complete the entire work? The number $n$ is a natural number; find it.