Average Speed is distance traveled divided by the time it takes to travel that distance, in this case:
v=2.48m/(6.3*10^-6s)
That's in units of m/s
To convert units, just multiply by 1, where 1 could be for example 60s/1min and 1 inch/.0254m
So v=(2.48m*60s*1inch)/(6.3*10^-6s*1min*.0254m)
Then you get speed in units of (m*s*inch)/(s*min*m)
m and s cancel top and bottom and you have units of inch/min.
