What is the standard deviation of hours worked, if the hours worked
per week are 43.9 and 1/3 of the workers work less than 40 hours per
week.  And what are the low and high numbers of hours worked per week
that represent 95% of the workers - assuming a standard deviation of 4
hours per week,

If you intended to say that the MEAN hours worked per week were 43.9,
and if we ASSUME that the hours worked per week are normally
distributed then this question can be answered.

The z score which 1/3 area is to the left is z= -.435
(40-43.9)/-.435  = 8.965 hours

In real life, I doubt this would follow a normal distribution. I'd
expect to se something bimodal. A group that works over-time and a
group that does not.

http://www.thefilehut.com/userfiles/echoproof/googleanswer/GA_01.xls