Interpret points relative to a system

Otto has some whipping cream that is $30\%$30, percent butterfat and some milk that is $2\%$2, percent butterfat. He wants to make a $500\,\text{mL}$500, start text, m, L, end text mixture of them that is $12\%$12, percent butterfat.

Here's a graph that shows a system of equations for this scenario where $x$x is the volume of whipping cream he uses and $y$y is the volume of milk he uses.