A 40 kilobase plasmid is numbered from 0 to 40 kilobases starting at the origin of replication. Restriction enzyme X cleaves the plasmid at 10 and 30 kilobases. Restriction enzyme Y cleaves the plasmid at 20 kilobases. How many bands would show if a solution containing plasmids digested using restriction enzymes X and Y is run through gel electrophoresis?