When necessary to use a ladder to accomplish work on a piece of equipment or to gain access to a specific area, the ladder shall be placed so that the base of the ladder is ____ of the working length of the ladder from the top support

When necessary to use a ladder to accomplish work on a piece of equipment or to gain access to a specific area, the ladder shall be placed so that the base of the ladder is ____ of the working length of the ladder from the top support