Step Stool

FIG. 1 is a perspective view of a step stool showing my new design; FIG. 2 is a front view thereof; FIG. 3 is a left view thereof; FIG. 4 is a right view thereof; FIG. 5 is a back view thereof; FIG. 6 is a top view thereof; and, FIG. 7 is a bottom view thereof. The broken lines shown on the drawings depict portions of the step stool that form no part of the claimed design.