Question 303078
let jack do the job in x hours alone

he does 1/x of the job in 1 hour

quinn does the same job in x/4 hours ( since he does the job 4 times faster)

4/x of the job he does in 1 hour

they together take 3 hours to do the job

1/3 of the job in 1 hour

1/x +4/x = 1/3

5/x= 1/3

x=15 hours jacks's time to do the job alone

Quinn does 4 times faster . he does in 1/4 time = 1/4* 15 = 15/4

=3.75 hours 

Ananth