What is the net force on a bright red mercedes convertible traveling along a straight road at a steady speed of 100 hm/h?

I don't know what " hm/h " means as a unit of speed. But if the bright red object is traveling in a straight line at a constant speed, then its acceleration is zero, and that means that the net force acting on it is zero. The same would be true of a car of any other color traveling with the same velocity.