6 pints of 20% pure fruit juice and 24 pints of 45 % pure fruit juice is mixed to get 30 pints of mixture of 40 % pure fruit juice
Solution:
The final volume is 30 pints of mixture of 40 % pure fruit juice
Let "x" be the volume of 20 % pure fruit juice
Then, (30 - x) is the volume of 45 % pure fruit juice
Then, we can say,
"x" be the volume of 20 % pure fruit juice and (30 - x) is the volume of 45 % pure fruit juice is mixed to get 30 pints of mixture of 40 % pure fruit juice
Therefore, we frame a equation as:

Solve the above expression for "x"

So, 6 pints of 20% pure fruit juice
Then, (30 - x) = 30 - 6 = 24
24 pints of 45 % pure fruit juice is used