Excel 2007 : average speed

hi all,

I am hoping that some one can help me,
I am using to excel 2007 to record my bike rides
and have it set up like;

Column A- is the date,
Column B- is the distance,
Column C- is the time,
Column D -is the route,
Column E- is the total kms
Column F -is the name of the bike,
Column G- is the total time

but I want to add another column to show my average speed
but do not know how to do this!

Hope someone can help

Ian