Final answer:
Sofia needs 1 1/3 cups of red paint to make 4 cups of purple paint.
Step-by-step explanation:
To make 4 cups of purple paint, Sofia needs to mix 4 times the amount of the original mixture. Therefore, to find how much red paint is needed, we can multiply 1/3 cup by 4:
1/3 cup * 4 = 4/3 cups
So, Sofia needs 4/3 cups or 1 1/3 cups of red paint to make 4 cups of purple paint.