She has a budget of $24 to spend on jewelry, so we know that the spending has to be less or equal than 24.
There is a spending that is already decided, and is $6 on a pair of earrings.
The rest will be spend on necklaces, wich cost $9 each one. If x is the number of necklaces, the spending on necklaces is 9x.
Then, the total spending is 6+9x and it has to be less or equal than 24, so we can write the inequality as: