Answer
a). The surface is not friction-less,
b). $32.7N$
Work Step by Step
a). Since the push is at constant speed, the sum of all forces acting in the direction parallel to the inclined plane is zero.
The surface to be friction-less, the pushing force must be equal to the weight component parallel to the surface.
So, this component =$mgsin\theta=35\times9.8sin20^{\circ}=117.3N$
So, the surface is not friction-less.
b). Friction force = $150-117.3=32.7N$
