1200
-------=171 miles per hour
7
Let
be the speed of the helicopter in still air. Let
be the speed of the wind. Then, from the given information,

Adding the above 2 equations,

The speed of the helicopter in still air 
Answer:
8 J
Explanation:
Heat = work + change in internal energy
Q = W + ΔU
15 J = 7 J + ΔU
ΔU = 8 J