TOPIC: Tire size for Aristocraft 19

Hi, I'm the new proud owner of an Aristocraft 19. It's a 1972 with the olive hardtop and 135hp chevy straight six. It's been in storage for the past 22 years and needless to say, the trailer needs new tires. I'm confused as to the size marked on the tires....
5.30/4.50-12. Tire dealers don't know what that means, either. Does it mean it will take either the 5.30-12 OR the 4.50? They are seriously dry rotted and I don't want to risk a blow out taking it to a lake for a test run. Any ideas?