The is c for this question
Answer:
The time required to finish the work by both candy and Tim working together = 36.83 minute
Step-by-step explanation:
Time taken by the candy to finish the work
= 85 min
Time taken by the Tim to finish the work
= 65 min
Thus the time taken by both to finish the work = 
Put the values of
and
we get ,
= 
= 
= 36.83 minute
Thus the time required to finish the work by both candy and Tim working together = 36.83 minute

check your calculator for the [!] factorial button.
also bear in mind that most calculators also have an [ₙPᵣ] button, to get Permuations, and you can just use that.