From 8:00 to 11:00, Mckenna spends 11:00-8:00 = 3 hours at work
When she joins the developers in the conference room for the meeting, she spends an additional 13:00-11:00 = 2 hours at work.
So far, she has spent 3+2 = <<3+2=5>>5 hours at work.
When she works for an additional 2 hours before heading home, her total work hours become 5+2 = <<5+2=7>>7 hours
#### 7