Finley makes 1 batch of her favorite shade of orange paint by mixing these paint amounts: 5

Finley makes 1 batch of her favorite shade of orange paint by mixing these paint amounts:

5 liters of yellow paint
3 liters of red paint
How many batches of orange paint can Finley make if she has 21 liters of red paint?
Finley has all of the yellow paint that she needs.