Claire sent us her solution (maybe she wanted to try the question because it's got her name in it!).

Claire has 24 cards, because 12x2=24.
Ross has 24 cards, because 8x3=24.
Lucia has 24 cards, because 6x4=24.
So they all have the same number of cards!

If you haven't learnt about multiplying yet, maybe you'd like to think about it like this.
Claire has 2+2+2+2+2+2+2+2+2+2+2+2=24 cards.
Ross has 3+3+3+3+3+3+3+3=24 cards.
Lucia has 4+4+4+4+4+4=24 cards.