Power is the rate of work that is done per time. Work is calculated from the product of force and the displacement. So, by using the definition of power and work, we can relate power with force, displacement and the time. We do as follows:
Power = Work / time
Power = Force x displacement / time
Power = 21 N (9 m) / 3 s
Power = 63 J /s = 63 W
The block on the action of two forces, the Force of Friction and the Tangential Weight. Using the Newton's Secound Law, we have:
Using the Velocity Hourly Equation, we get:
Uniting the equations:
Entering the unknowns:

Obs: Approximate results
If you notice any mistake in my english, please let me know, because i am not native.
Answer:
a. The primary turns is 60 turns
b. The secondary voltage will be 360 volts.
Explanation:
Given data
secondary turns N2= 40 turns
primary turns N1= ?
primary voltage V1= 120 volts
secondary voltage V2= 8 volts
Applying the transformer formula which is

we can solve for N1 by substituting into the equation above

the primary turns is 60 turns
If the primary voltage is V1 240 volts hence the secondary voltage V2 will be (to get the voltage of the secondary coil using emf substitute the values of the previously gotten N1 and N2 using V1 as 240 volts)

the secondary voltage will be 360 volts.