What is the steepest incline that can be climbed by a car at constant velocity if the coefficient between the tires and the road is .60?

Let theta = angle of inclination
What are the forces on the car? There are three forces
1. Force of gravity vertically downward
2. Normal force perpendicular to the incline
3. Friction force up the incline
Friction force = 0.60 * normal force
Resolve all forces perpendicular to incline and make the resultant as zero
Also resolve forces parallel to incline and make the resultant as zero
From these equations, you will know the value of theta

Do you understand why in this problem a constant speed of the car is mentioned?