Answer:
18
Step-by-step explanation:
Let's say x is the volume of the 65% solution.
Amount of alcohol in the 65% solution + amount of alcohol in the 25% solution = amount of alcohol in the 40% solution
0.65 x + 0.25 (30) = 0.40 (x + 30)
0.65 x + 7.5 = 0.40 x + 12
0.25 x = 4.5
x = 18
You need to add 18 liters of the 65% solution.
