Answer:
9:20 am
Explanation:
The cycles will coincide again at the least common multiple of the cycle times.
20 min = 4 × 5 min
16 min = 4 × 4 min
The least common multiple of these times is 4 × 4 × 5 min = 80 min. 80 minutes after 8 am is 9:20 am.
The two buses will next leave at once at 9:20 am.