Johanna is mixing red and blue paint to make purple paint for her bedroom. the amount of red paint and blue paint she needs is directly proportional to each other. if she uses three pints of blue paint and five pints of red paint, it makes the perfect shade of purple to match her bed comforter. johanna wants to make one more batch of purple paint in the exact same shade. if she only has 15 pints of red paint left, how much blue paint does she need?