Air balloon #1 is 10 meters above the ground rising 15 meters per minute. Air balloon #2 is 150 meters about the ground descending 20 meters per minute in how many minutes will the balloons be at the same height
When the 2 Balloons meet, they will be at the same height FROM THE GROUND :
Distance travelled by #1 : 10 + 15.Time Distance travelled by #2 : 150 - 20.Time (the descending speed is negative) Since it's the same distance from the ground, we can write: