If the party-goers each get 3 party packs then the boys will get 3×15=45 packs while the girls get 3×18=54 packs. The party-goers get 45+54=99=3(15+18) packs between them.
54-45=9 packs, so the girls get 9 more party packs than the boys.
So Katlego's statement is only true if each party-goer gets 3 party packs.
For example, if each party-goer gets only one party pack then the girls get 18-15=3 more packs between them than the boys.