Answer:
4180 N
Step-by-step explanation:
In order to keep the truck balanced and stationary, the force of friction on the truck must be equal to the component of the weight of the truck acting parallel to the slope.
The component of the weight of the truck acting parallel to the slope is:

where
m = 3500 kg is the mass of the truck
g = 9.8 m/s^2 is the acceleration of gravity
is the angle of the slope
Therefore, the force of friction must be equal to
