Apply when a stepladder is placed as shown,
is it possible for the lower ends of the ladder to
be 12 feet apart? explain.

The correct answer is:

Open the compass and mark two points of intersection between arcs from the given line.

Explanation:

We start out from a point on the line, swinging the compass around to intersect our line twice.

We then set the compass to a width wider than the one we began with.  We move the compass to one of the points of intersection with one of the arcs and our line, and construct an arc below the original arc.  Keeping the width of the compass the same, we move to the other point of intersection and draw another arc that intersects the one we just drew.  We then use a straightedge to draw a line through the point of intersection of these two smaller arcs and the original point on our line.