Pathfinder 1E Mirror Image macro

I apologize in advance if this is a bit noobish. I've been playing casters a lot recently and been using Mirror Image a tonne. It gives me a 1d4 + 1 per three caster levels I have. Is there a way that I can use the [[1d4+ and some code here ]] to have it automatically tell me how many images I'll get when I click on the spell? This stuff isn't my strong suit, I'm afraid. ^^;;

I put this in the effect line of mirror image: [[1d4+floor(@{level}/3)]] images maximum 8. In case you multiclass, it should probably be: [[1d4+floor(@{class1_level}/3)]] images maximum 8.