Answer:her breaststroke speed is is 30 laps per hour
Explanation:
Let b represent Justine’s butterfly speed and
Let r represent Justine’s breaststroke speed.
Justine swims freestyle at a pace of 150 laps per hour. Justine swims breaststroke 20 laps per hour slower than she swims butterfly. This means that
r = b - 20
If Justine’s freestyle speed is three times faster than her butterfly speed, it means that
3b = 150
b = 150/3 = 50
Substituting b = 50 into r = b - 20, it becomes
r = 50 - 20 = 30