The speed of sound is 760 mph at sea level, my dad was an aircraft technician for 24 years, he knows what he is talking about. Plus the fact, I already knew it was anyway.
The speed of light changes when it goes through a different medium, it goes slower through water than air, and slower through glass than air. The angle of which the light enters the glass decides which angle it will come out at.
At 46 degrees and above it is total internal reflection which reflects the light instead of refracting, the light still changes speed. Ask your teacher.