A friend asked me for help with this math problem. I immediately got the answer by figuring it in my head, but that does not help my friend. I need to be able to show the equation one would set up to solve this problem. Again, I am not looking for the answer but HOW to get the answer. The word problem: How much of a 50% salt solution would you add to 40 liters of a 20% salt solution to get a 35% salt solution?