OK,
A1: 4
B1: 10:25
C1: 5122
D1: =(B1*C1)/A1
formatted as time, D1 returns 00:00:29 man-hours per case.
If you want to work in decimals rather than times, multiply B1 by 24 to
get 10.4166667 hours. Then D1 (formatted as general, or some other
Number format) returns 0.00813484 man-hours per case.