Achemistry 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