Answer:
480 mph and 600 mph
Step-by-step explanation:
we can call the first planes speed x, and the other x+120 because it is going 120 mph faster. Because distance = rate * time, that means that 1620 = 1.5*(x+x+120) and then you just solve the equation
1620=1.5*(x+x+120)
1620=1.5*(2x+120)
1620=3x+180
1440=3x
x=480
x+120=600