At maximum speed, an airplane travels 1680 miles against the wind in 5 hours flying with the wind, the plane can travel the same distance in 4 hours. let x be the maximum speed of the plane and y be the speed pf the wind. what is the speed of the plane with no wind

X = velocity of plane

y = velocity of wind

x - y = 1680/5 = 336 mph ... (1) [ plane flying against the wind]

&

x + y = 1680/4 = 420 mph ... (2) [ plane flying with the wind]

Adding (1) and (2) to eliminate y gives

2x = 756

x = 378 mph is the speed of the plane with no wind.