distance = speed * time
so plug in your numbers
how long does it take light travelling at3*10^8 m/s to across a room 6 m long?
3 answers
Time=distance/speed
=6/3×10^8
=2×10^-9seconds
=6/3×10^8
=2×10^-9seconds
looks more like 2*10^-8 to me.