Answer:
Step-by-step explanation:
let the speed of one plane=x mph
speed of other plane=x+120 mph
x×1.5+(x+120)×1.5=1620
(x+x+120)×1.5=1620
(2x+120)×1.5=1620
3x+180=1620
3x=1620-180
3x=1440
x=480
speed of one plane=480 mph
speed of second plane=480+120=600 mph