If an airplane is flying at 300 km /h to the east and is facing a headwind of 18.0 km/h what is the airplane's final velocity

Explanation:

Airplane is moving with speed of 300 km/h

so this is the absolute speed with which airplane by which it can fly in still air

so here if air is also moving with some speed then the net speed of the plane in ground frame would be different

So here we can say

now when head wind is blowing then in that case the speed of plane is opposite to the motion of the plane

so here we have

find the sum of the two horizontal vectors and the sum of the two vertical vectors

isoceles right angled triangle