First find the total amount of time Marcus spends blow-drying his dog: 20 minutes / 2 = <<20/2=10>>10 minutes
Then find the time Marcus spends walking: 3 miles / 6 miles/hour = <<3/6=.5>>.5 hours
Then convert that time to minutes: .5 hours * 60 minutes/hour = <<.5*60=30>>30 minutes
Then add up the time Marcus spends washing, drying and walking to find the total time: 10 minutes + 20 minutes + 30 minutes = <<10+20+30=60>>60 minutes
#### 60