The quickest way to figure this out is to think which numbers are multiples of the first number. 7 to 12 is not a 7 dollar difference so no. 6 to 12 is 6 so yes. 12 to 18 is 6 so yes. 18 to 24 is 6 so yes. Now to the next, 5 to 5 is not a 5 difference, so no. 1 to 4 is not a 1 difference so it's wrong. The only one that is right is student b.