Question 412931
Marissa ----- 8 days
so she does 1/8 of the job in 1 day
..
assistant ----- 12 days
she does 1/12 of the job in 1 day.
...
together they do 1/8 + 1/12 of the job in 1 day
=5/24 of the job in 1 day.
so in 4 days they will do 
4*5/24 of the job
= 5/6 of the job in 4 days.