Well, since there are 5 cups of oatmeal, and she eats 1/3 a day, then the equation is: 5 divided by 1/3 then change 1/3 to its reciprocal which is 3. 5 times three is 15 so therefore Stella will finish it in 15 days.
I say it is a red marble because as you said, there are 10 red marbles and 6 blue ones and since there are 4 more red marbles, there is a higher perchentage of it being a red marble . (I hope i answered your question)
