Populate data only when project is "complete"

Hi guys,

I am putting the finishing touches on a spread sheet and only have one last thing to do. Attached is a spread sheet for reference.

You will see in the April tab that there is a box with "Comp" labeled at the end of the data. Once a particual project has been complete the idea is to put an x (or otherwise marked) in that box and have the totals page only count those numbers IF the project is complete. Anything that does not have the x in the completed box should not transfer to the total tab.

One problem I am running into is that I already have formulas in the cells of the totals tab so I'm not sure how to put multiple forumlas into a cell or if it can be done.

I have been searching thru the forum to see if I could figure this out on my own but I'm not coming up with anything that seems like it would work in my situation. Any help on this would be a huge benefit, my boss wants this spread sheet done ASAP - as most bosses do

Thank you!
Andreahelp1.xlsx