Answer:
It's the 2nd one
Explanation:
To find the number of yellow marbles, you would do the number of blue marbles plus 6 marbles.
So in this case, let's say n was equal to the number of blue balls, the equation would be n+(n+6)=24.
What if n was equal to the number of yellow balls. The equation would be n+(n-6)=24.
Hope this made sense, let me know if you are still confused.