Sarah has whole milk, which contains $3.25\%$ butterfat by volume, and one type of low-fat milk, which contains $1\%$ butterfat by volume. Which of the following systems could be used to determine the amount of whole milk, $w$, in ounces, and the amount of low-fat milk, $l$, in ounces, that Sarah should mix to obtain $32$ ounces of a low-fat milk with $2\%$ butterfat by volume? [[☃ radio 1]]