An aircraft travels upwind with a speed of 420 mph for 7 hou

An aircraft travels upwind with a speed of 420 mph for 7 hours. In how muchtime will it cover the same distance in absence of wind? Wind speed is 120 mph.

Solution

let x=speed of plane with no wind
let t=travel time of plane with no wind
x-120=speed of plane against the wind
travel time*speed=distance
7*420=2940 miles
..
7(x-120)=2940
7x-840=2940
7x=3780
x=540 mph(speed of plane in absence of wind)
..
travel time=distance/speed
t=2940/540
t=5.44
travel time of plane in absence of wind=5.44 hrs