How do I subtract a # field from a time field

[noaspenwin]

i have a number field that I need subtracted from a time formatted field. What conversion function do I use in order to do the math.

total_day_hours (number field) - total_break_time (time field) = total_hours_worked (? don't know how to get this total)

[-Queue-]

total_day_hours - Hour(total_break_time) - Minute(total_break_time)/60

[noaspenwin]

Thanks Much !