If Travis already has passed 11, and Jennifer has already passed 2, then we just add 2 to Travis and 5 to Jennifer x amount of times until they have passed the same amount of tests. So:
Travis: 11 Jennifer: 2
Week1 + 2 + 5
Week2 2 5
Week3 2 5
------- --------
17 17
So= it will take 3 weeks for them to have both passed a total of 17 tests each.