Clarissa is not correct. If she were to choose one from the stack at random, it means that she has a 25%, or a 1/4 chance to pick the oatmeal, just like the other breakfast items.
If there were to be more oatmeals than any of the other items, it will heighten the chance of her getting oatmeal which would be the only way to make her statement correct.
You need to subtract 6 from 24 because it’s the inverse operation of addition which will help you find the unknown value, x.
