Hello, RTC1996!

Please check the wording of the problem.

As written, the problem is truly silly . . .

One ounce of the mixture containing 6% salt

is to be mixed with two ounces of a mixture which is 15% salt

in order to obtain a solution which is 12% salt. . This is true.

What is the percentage of salt in the resulting solution?

I'll take a wild guess . . . um . . . twelve percent?