(a) 800-16 = 784 (the distance between16m and the departure in the opposite direction at the same time mean that16m is unnecessary to fly).
784 divided by (16+ 12)=28 (seconds) Speed equals distance divided by time.
A: It took 18 seconds for two hot air balloons to meet for the first time.
(B) 16 divided by 16= 1 (A is in front of B 16m, which means A flies ahead of time 1 sec).
Next, find the least common multiple of 16 and 12 by short division. Unfortunately, I don't know how to send short hair on it, otherwise the effect will be more obvious.
A: It took 48 seconds for two hot air balloons to meet for the first time.