Explanation:
The aircraft is traveling north at 100 m/s.
The wind blows from the west (towards the east) at 25 m/s.
The two vectors form a right triangle. The magnitude of the resultant velocity can be found with Pythagorean theorem:
v² = vx² + vy²
v² = (25 m/s)² + (100 m/s)²
v = 103 m/s
The direction can be found with trigonometry:
θ = atan(vy / vx)
θ = atan(100 / 25)
θ = 76.0°
The resultant velocity is 103 m/s at 76.0° north of east.