Answer:
106.1 m/s
Step-by-step explanation:
The shadow of the plane is moving at the same velocity as the horizontal component of the airplane's velocity.
The horizontal component of the airplane's velocity is

where
v = 150 m/s is the velocity of the airplane
is the angle between the airplane's velocity and the horizontal
Substituting,

So, the shadow is moving at 106.1 m/s as well.