You mix 1/4 cup of juice concentrate for every 2 cups of water to make 18 cups of juice. the amount of concentrate and water can be solve by establishing an equation:
2x + (x/4) = 18 where x is the number of times you mix the both.
Since x = 8
The amount of water 2(8)= 16 cups
Amount 0f concentrate (8/4) = 2 cups