I work at a tint shop, the law on paper is that the entire side of the car has to be 35% and the back window can be whatever you want.
However, we tint cars with 30% on the front (meters can't usually tell the difference between 35 and 30) and then we do whatever the customer wants on the back sides/quarters and the back window. Basically if the front two windows are 30% or greater, you won't get any hastle.