A small planar mirror is attached to a thin vertical wire so that the mirror is parallel to a wall 1.0 m away. A horizontal scale is mounted flat on the wall opposite the mirror, whose center is directly opposite the zero mark on the scale. A horizontal laserbeam reflects off the mirror and hits the scale at 5.0 cm left of zero. The mirror is then rotated through an angle a and the beam-scale spot of light moves left an additional 15.0 cm. Find α.