Does fg increase or decrease when one mass increases

A10.0 kg cart and a 15kg cart are locked together with a compressed spring between them. they are then released so that the spring pushes the two carts apart. the 10.0 kg cart is moving at 4.5 m/s afterward. how fast is the 15kg cart moving? 3.0 m/s 2.0 m/s 4.5 m/s 5.0 m/s

With i really need the correct answer!

Light traveling in a medium with a refractive index 1.19 is incident on a plate of another medium with index of refraction 1.79. at what angle of incidence is the reflected light fully polarized?