Question 929653
set e = rate of an experienced mover in jobs per hour
 i = rate of an inexperienced in jobs per hour

We have 4e * 3 hours = 1 job
and 6i * 4 hours = 1 job

First work with 4e * 3  = 1
 12e = 1
 e = 1/12 jobs per hour

Now work 6i * 4  = 1 
 24e = 1
 i = 1/24
So for all working together
 (6(1/24) + 4(1/12))y = 1
 ( 1/4 + 1/3 ) y = 1
 ( 3/12 + 4/12 )y = 1
 ( 7/12 )y = 1
multiply each side by 12/7
 y = 12/7 hours = 1 5/7 hours