On Mondays, he walks 6 miles at 2 miles per hour, for a length of 6/2=<<6/2=3>>3 hours.
On Wednesdays, he walks 6 miles at 3 miles per hour, for a length of 6/3=<<6/3=2>>2 hours.
And on Fridays, he runs 6 miles at 6 miles per hour, for a length of 6/6=<<6/6=1>>1 hour.
The combined total time he spends exercising in a week is 3+2+1=<<3+2+1=6>>6 hours.
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