Finding work day lead time using networkdays function across multiple sheets

I need help figuring out a formula that can find the work day lead time between two dates. My data consists of a date when a job is entered into the system, and an end date when the job is completed. I want to find the time it took to complete the job, excluding weekends and holidays. The first sheet is all my data, the second sheet is my results page, and my third sheet is my setup sheet where I figured out the network days formula.

I just cant figure out how to use the network days formula in conjunction with my data to find my actual lead time.

I tried this formula =AVERAGE(IF((Data!K3:K99960>=A3)*(Data!J3:J99960<=B3),Data!P3:P99960)) where K is my start date, J is the end date, and P is the total days to install including weekends/holidays, but it isnt working.
Looking at it now I dont even think I'm close to the right formula for what I am trying to get.
Thanks for any help.

Date Complete Date Created Total Days to Install
2/27/2017 2/17/2017 10
2/27/2017 2/22/2017 5
2/27/2017 2/21/2017 6
2/27/2017 2/14/2017 13
2/27/2017 2/17/2017 10
2/27/2017 2/20/2017 7


So this is the data I am working with. Currently I am using this formula to get the Total days to install figure, =DATEDIF(K14,J14,"d"). This gives me the total days in between the dates, where I am trying to just get the work/business days.

Then I am taking the total days to install data and getting the average between a range of dates, a normal work week, using this formula =AVERAGE(IF(ISNUMBER(P1:P2),P1:P2))

OK, so that worked, but there are some times where I dont have a completion date, so that cell is empty. Using the network days function that is giving me these huge negative numbers, which is now throwing off my lead time average.
This is the formula I was using, but now it is not accurate.
=AVERAGE(IF(ISNUMBER(P3:P10),P3:10))
I tried doing this
=AVERAGE(IF(ISNUMBER,">=0"(P3:P10),P3:P10))
but that is giving me an error.

Would this be the best formula to use then?
=AVERAGEIF(P3:P10,">=0")

Thanks for all the help so far.