Two flat mirrors (M ₁ and M ₂) are perpendicular to each other. A monochromatic, laser beam hits the surface of M ₁, at an angle θ, 15.0 cm from the intersection of the two surfaces. After reflection from M ₁, the beam of light hits the surface of M ₂ 25.0 cm away from the intersection. Determine the angle of incidence θ .