Answer: 21 quarts of blue paint
Step-by-step explanation: To make a batch of purple paint, it is necessary 2 quarts of red and 3 quarts of blue, resulting in 5 quarts of purple.
So, to make 35 quarts of purple:
5x = 35
x = 7
It is needed, in total, 7 quarts of purple.
As, the ratio is 2 quarts of red to 3 quarts of blue:
Blue: 7 x 3 = 21
For 35 quarts of purple paint, it's necessary 21 quarts of blue paint.