Trouble with absolute values and hours/minutes and formulas

I am trying to put together a spreadsheet with call times for our inside sales team. I cannot get the formulas to work and know I am doing something wrong with the formatting of the dates. What I am trying to do (and I will attach the spreadsheet below) is:

Total talk time (right now is expressed as a number, which I know it shouldn't be) --so E4, should be hours and minutes, so 35 hours and 25 minutes

Days this month is an absolute value, so $D$3 in this example

subtract the days off and the meeting days off (so B4 and C4 together)

What I've tried to do is =E4/($D$3-(B4+C4)) to figure out the average talk time.

Does not work and I've tried a whole bunch of different formulations of it. I'm sure I don't have the duration time correct. Can anyone assist?

Thanks,

dglazer