VLOOKUP to find multi results and sum adjacent cells

Hi everyone, it's been a while since I was last here. I am completely stuck on this one... any help would be great!

I have a timesheet and I enter project numbers during the day and it calculates the time on each. The problem is that some have multiple entries that are not consecutively entered and VLOOKUP will only return the first entries time and not the others below.

My spreadsheet is attached for reference... Any help is greatly appreciated.

Thank you.

ATTACH]242432[/ATTACH]