Answer: 70.5 km/h
Justification:
The question is not clearly stated but it seems you are asking for the x - component of the velocity of the helicopter.
You can find the x and y - components of the velocity using the trigonometric ratios sine and cosine.
The sine ratio relates the y-component and the velocity by:
sin(angle) = y-component of velocity / velocity
The cosine ratio related the x-component and the velocity by:
cos(angle) = x-component of velocity / velocity.
Since you have the angle and the velocity and are asked by the x-component of the velocity, you need to use the cosine ratio:
cos(35°)= x-component / 86.0 km/h
=> x -component = 86.0 km/h * cos(35°) = 70.5 km/h
The velocity of the aircraft relative to the ground is 240 km/h North
Explanation:
We can solve this problem by using vector addition. In fact, the velocity of the aircraft relative to the ground is the (vector) sum between the velocity of the aircraft relative to the air and the velocity of the air relative to the ground.
Mathematically:

where
v' is the velocity of the aircraft relative to the ground
v is the velocity of the aircraft relative to the air
is the velocity of the air relative to the ground.
Taking north as positive direction, we have:
v = +320 km/h
(since the air is moving from North)
Therefore, we find
(north)
Learn more about vector addition:
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