Answer:
approximately 7 days.
Explanation:
Don takes time to complete 4 jobs = 3 days
he completed his job in 1 day =
Lily takes time to complete 5 jobs = 2 days
Lily completed her job in 1 day =

Working together they can complete the job in 1 day
=

=

=

Working together it will take time to complete 25 jobs
= 25 ÷

=

=

=
days
= 6.52 ≈ 7 days
It will take 6.52 or approximately 7 days to complete 25 jobs together.