A BILLBOARD PAINTER HAS BEEN ASSIGNED THE TASK OF CHANGING THE ADVERTISMENT ON A 20-FT BILLBOARD,THE BOTTOM OF WHICH IS 15FT OFF THE GROUND.AFTER EXAMINING THE SITE, SHE IDENTIFIES TWO AREAS ON THE GROUNG UNDER THE SIGN THAT ARE STURDY ENOUGH TO SUPPORT HER LADDER. ONE ARE IS 10-FT FROM THE BASE OF THE BILLBOARD AND THE OTHER IS 15-FT FROM THE BASE..