If you are being assigned this type of problem, you should have covered how to work with forces at angles by using trigonometry. The car's weight is the result of the mass of it times to acceleration to gravity directed straight down. The force of the car along with hill isn't this number though. Think of the hill as the hypotenuse of a right triangle. You know the angle and the vertical leg of the triangle, so finding the hypotenuse should be simple.