You're asking what the stock tint on the rear 3 windows is, right? It should be between 15-20%. If the law truly is 35% all around for everything, then it's already darker than the limit and that wouldn't allow you to put anything else on.
I would check your laws for sure to see what is legal. Most states have no restrictions on the rear windows, but a lot still do. Other states exempt trucks, SUVs and vans from the rear restrictions since their factory tinted rear windows are often already darker than what the state law allows.