15 !
the diagram shows a stage in the construction of a line perpendicular to line gh through point a. the next step in this construction is
a.) to set the compass width to line line segment ga and draw arcs centered at h across both sides of the line.
b.) to use sufficient compass width and draw an arc centered at a crossing the previous arc.
c.) to set the compass width to line gh and draw an arc centered at a crossing the previous arc in the image.
d.) to keep the same compass width and draw an arc centered at h crossing the previous arc in the image.