The combined length of all the rope is 41 feet because 8 + 20 + (2 x 3) + 7 = <<8+20+(2*3)+7=41>>41
He loses 6 feet from the knots because 5 x 1.2 = <<5*1.2=6>>6
The final length is 35 feet because 41 - 6 = <<41-6=35>>35
#### 35