Find the wind velocity if course 060 degree, airspeed 250km/h; track 040 degree, ground speed 260km/h.

To find the wind velocity, we need to compare the course and track with the airspeed and ground speed, respectively.

1. Let's start by understanding the terms involved in this problem:
- Course: The direction in which an aircraft is pointing or heading.
- Airspeed: The speed at which an aircraft moves through the air.
- Track: The direction an aircraft is actually moving over the ground.
- Ground speed: The speed at which an aircraft moves relative to the ground.

2. In this problem, we are given:
- Course: 060 degrees
- Airspeed: 250 km/h
- Track: 040 degrees
- Ground speed: 260 km/h

3. The difference between the course and the track is caused by the effect of wind. By finding this difference, we can determine the wind velocity.
- Course correction angle = Course - Track
- Course correction angle = 060 - 040 = 20 degrees (clockwise)

4. The wind is blowing in the opposite direction of the course correction angle. Therefore, the wind direction is 200 degrees (opposite direction).
- Wind direction = Course - Course correction angle = 060 - 20 = 040 degrees

5. To calculate the wind velocity, we can use trigonometry. We'll use the law of sines to find the wind speed:
- sin(wind direction) / wind speed = sin(course correction angle) / ground speed
- sin(40 degrees) / wind speed = sin(20 degrees) / 260 km/h

6. Let's solve the equation:
- wind speed = (sin(40 degrees) * 260 km/h) / sin(20 degrees)
- wind speed ≈ 163.33 km/h

Therefore, the wind velocity is approximately 163.33 km/h. The wind is blowing from 200 degrees at a speed of 163.33 km/h.