A dad takes his kids to their school just 8.0 miles down the road but with traffic it takes him 30 minutes and the fastest he can go is 35 mi/hr. One of his children has forgotten his lunch, so the dad goes back, gets the lunch, and returns to the school. It takes him just an additional 30 minutes since traffic has cleared. What is his average velocity for the morning?
A 8 mi/hr
B 16 mi/hr
C 24 mi/hr
D 35 mi/hr