Answer :
I think they will meet in 4 minutes.
Explanation
10+15+15+15+15=70
150-20-20-20-20=70
Every minute the first balloon goes up 15 meters and the second balloon goes down 20 meters.
Explanation
10+15+15+15+15=70
150-20-20-20-20=70
Every minute the first balloon goes up 15 meters and the second balloon goes down 20 meters.