Question 450568
John found his plane could fly at 6 times the speed of the wind. He flew 700 miles upwind in 3 hours more than it took to fly 560 miles downwind. What was the speed of the plan in still air?"
upwind=against the wind
let 
wind=w
downwind=+w
upwind=-w

p=plane
p=6w
r*t=d
(p-w)(3+t)=700
(p+w)t=560
(6w-w)(3+t)=700
(6w+w)t=560

(5w)(3+t)=700
w*(3+t)=140

(7w)t=560
wt=80
w=80/t
w=140/(3+t)
80/t=140/(3+t)
4/t=7/(3+t)
4*(3+t)=7t
12+4t=7t
12=3t
4=t
wt=80
w=20
p=6*w=120 in still air