An airplane travels east at an air speed of 400.0 m/s into a head wind of 35.0 m/s. What is the airplane's ground speed?

Velocity of the plane relative to the air = + 400.0 m/s

Velocity of the air relative to the ground = - 35.0 m/s (negative because it's moving opposite to the eastward direction)

Velocity of the plane relative to the ground = (velocity of the plane relative to the air) + (velocity of the air relative to the ground) = 365.0 m/s to the east