To create an ink refresher for dye-based ink, some crafters will mix pure vegetable glycerine with water to get a mixture that is \(12\%\) vegetable glycerine, by volume. Kathy does not have pure vegetable glycerine, but she does have
a \(90\) mL mixture that is \(10.5\%\) vegetable glycerine,
a \(120\) mL mixture that is \(30\%\) vegetable glycerine, and
a \(1\) L mixture that is \(7.5\%\) vegetable glycerine.
Since Kathy is a math teacher, she knows she can use the contents of these three mixtures to create a mixture that is \(12\%\) vegetable glycerine, by volume. She combines the contents of the entire \(90\) mL mixture with the contents of the entire \(120\) mL mixture, and then adds some of the \(1\) L mixture. How many millilitres of the \(1\) L mixture should she add to create a new mixture that is \(12\%\) vegetable glycerine, by volume?