Step-by-step explanation:
Step 1: Question statement and Inferences
Let x liters of the 60% solution be added.
So, amount of Alcohol in this solution = 60% of x = 0.6x L
Now, let us consider the 40% solution.
The total volume of this solution is 50 L
So, amount of Alcohol in this solution = 40% of 50
 
Step 2: Finding required values
When x L of 60% solution are mixed with 50 L of the 40% solution, the total volume of the resultant solution will be (50+x) L
By the Law of Conservation of Mass,
Amount of alcohol in the input solutions = Amount of alcohol in the final solution
=> Amount of alcohol in the final solution = 20 + 0.6x
So, concentration of Alcohol in the final solution

Step 3: Calculating the final answer
It is given that the concentration of alcohol in the final solution is 50%

