Answer:
1250 N
Explanation:
length of wrench = 20 cm = 0.2 m
Write the length of wrench in vector form
r = 0.2 j metre
Direction of force= 
Let the magnitude of force is F
So, write the force in vector form
F = F 
torque, T = 150 Nm
Torque = T = r x F

F = 1250 N
Thus, the magnitude of force is 1250 N.
The guy below is wrong!
F=ma
Where force = mass x acceleration
We dont have acceleration, a= change in velocity divided by the time taken.
a = v (final velocity) - u (initial) / t
a us 8-0 (at rest means u was 0) / 20 = 0.4
Using F=ma
F= mass x acceleration
F= 4 x 0.4
F=1.6 N