Still no. 8 hours of sleep a day leaves you 16 hours a day, so 112 hours a week. 40 hours is 36% of 112. And, yeah, you could throw in commute time and get a higher percentage. It still wouldn't get you 71%, though.
What skersten did is 5/7 = 71%, as if any day you work on is totally lost to you for any other purpose.
