Answer:
She will finish in 12 hours.
Step-by-step explanation:
∵ The time taken by Sarah and Tim when they work together = 4 hours,
∴ The one day work of both Sarah and Tim =

Now, time taken by Tim when he works alone = 6 hours,
So, his one day work =

Thus, the one day work of Sarah = Their combined work - one day work of Tim



Hence, the time taken by Sarah when she works alone =


= 12 days.