I need to Formulate two application (real-world)( linear not Volume) problems that can be solved with a system of equations in either 2 or 3...

I need to Formulate two application (real-world)( linear not Volume) problems that can be solved with a system of equations in either 2 or 3 variables.  The problem statement has to be sure to include all of the information necessary to write down the governing system of equations.