The document discusses expressing an interval in set-builder notation and graphing it on a number line. The specific interval given is (-9,-1]. It provides the solution that in set-builder notation the interval is represented as {x | x > -9 and x ≤ -1} and when graphed on a number line it is shown as a line from -10 to 0 with an open circle at -9 and a closed circle at -1.