There are two word problems that are giving me alot of trouble for an assignment that I have to do.

A 50% saline solution mixed together with a 30% saline solution to get 30L of a 46% concentrated saline solution. How many litres of each are needed to be mixed?

You invest a total of $1800 into two diffrent investments. One investment returned 9% and the other returned 6%. If the interest on the 9% was $102 more of a return than the return of the 6% investment then how much of your $1800 was in each seperate account?

I don't know how to set up any of these problems. If I could have help with the set up I could do it. These are the only problems on the sheet giving me problems. Thanks for your assistance.