In the question about the car stopping: Vf=Om/s. You can use vf^2=vi^2+2aΔx to get x, the stopping distance. To get a use the frictional force Ff = µFN. You’ll have to decide which µ works better.
For the box on the slope: amazingly you can do it even though you don’t know the mass of the box. The mass will cancel out everywhere. Start with ma = Fnet = Fparallel-Ff. (FN = Fperp.) If you substitute in correctly, you can get mass to cancel.
Sorry about the lack of subscripts and superscripts here. Did you see the extra credit assignment.
