A chemistry teacher needs to mix a 30% salt solution with a 70% salt solution to make 20 qt of a 40% salt solution. How many quarts of each solution should the teacher mix to get the desired result?

The formula should be 0.3x + 0.7 (20-x) = 0.4 (20)

Simplifying it would get 3x + 7 (20-x) = 4 (20)

and: 3x + 140 - 7x = 80

then: 4x = 60

x = 15

So then for the 30% solution: 15 quarts

And for the 40%: 5 quarts