A car skidded off the road and hit a low stone wall. Gl from the windscreen was found 4.0 m in front of the?

The key issue here is the loss of kinetic energy due to the deformation of the windshield (into pieces). Whenever you have deformation, you have a so called "nonconservative" energy loss into heat. Momentum is conserved, but sometimes energy goes into heat, which is a whole different ball game (see Thermodynamics). So the third opinion is the best.