Round Robin Wait time

[vorticalbox]

so in uni today we have been doing about scheduling, and we were given a task to work out the wait time with a quantum of 7. Now i believe i have created the gannet chat correctly (be sure to correct me if i haven't as we weren't actually told how to create them). Now my lecture tells me the answer is 13 average however he hasn't told us what formula to use to calculate it and i get 11 as the average.

 

What I have so far is attached in the screen shot. 

 

p1 = 0 + (14-7) = 7

p2 = (8-6) = 2

p3 = (16-9) = 7

p4 = (21-10)+(35-27) = 19

p5 = (28-15) + (41-34) = 20

 

average wait time = 11

[vorticalbox]

Do I need to add burst time to the totally wait time?