Let y be the amount of paint in the yellow flask, r be the amount of paint in the red flask in cups. We are given y = r. I'm going to skip to B since A is interpretation.
B. Let y = r = 2. (simple enough number to use)
If one cup of red paint is mixed thoroughly into the yellow flask, we have that y = 3, with part red paint part yellow paint and r = 1, 1 cup red paint.
If one cup of mixed paint from the mixed paint from the yellow flask is mixed into the red flask, we have that y = 2, with part red paint part yellow paint (concentration doesn't change given it was mixed thoroughly) and r = 2, with the following concentration.
1 cup + 1/3 cup red paint, 2/3 cup yellow paint (out of 2 cups). Hence the concentration of red paint is and the concentration of yellow paint is