we need a proportion to get equavalent quantity
initially he needs 2 red pints and 3 yellow pints
if he wants use 9 yellow pints means that multiplies the 3 yellow pints by 3 if we need a proportional quantity we need to mutiply by the same number so
the red pints by 3 too
and 2x3=6
then , he needs 6 red pints for 9 yellow pints
in total 15 pints
