A store gave away a $5 gift card to every sixth customer and a $10 gift card to every tenth customer.Which customer would be the first one to receive both a $5 and a $10 gift card?please help

i do not understand

Multiples of 10:

10, 20, 30, 40

Multiples of 6:

6, 12, 18, 24, 30, 36, 42

30

Customer number 1

Customer number 2

how do you do this problem

the gcf of both these numbers is 30 so the answer would be 30