Is there maths that tells us how often you should 3bet against an opponents range??

Say I'm heads up and someone is opening 80% of hands how do I workout how much I should 3bet him?? It's obviously going to be more than 3betting someone in 6max who's opening tighter. But how much more??

The reason I ask is becasue I'm really bad at adjusting to players with different ranges, I just play the same against everyone. which doesn't feel right.