If theres only two colors, red and blue and for every six people who prefer red, there are six people who prefer blue then divide 48 in half and he should order 24 red pens and 24 blue pens.
Domain refers to the set of possible input values, the domain of a graph consists of all the input values shown on the x-axis. The range is the set of possible output values, which are shown on the y-axis.