Since u said the back window tint is bubbling up, I would take off all the old tint on all the windows and get it replaced with the darker tint. I would get 20% tint. I have 20% tint on all of my windows except windshield and I've never been pulled over. Where I live the law is 50% front and 35% back. 20% tint is dark but u can still see inside the car or if u wanna stay clear from the cops I would get 35% tint. 35% tint is almost clear but u can still kinda tell there is window tint on the windows.