Question 1016229
Starting by calling the rate of the car r, the rate of the plane r+100 and with rt=d, we can write
rt = 280
or t = 280/r
(r+100)t = 680
or t = 680/(r+100)
Set these equal and get
280/r = 680/(r+100)
Now cross-multiply and solve
680r = 280r + 28000
400r = 28000
r = 70 mph
r+100 = 170 mph, the rate of the plane...