I had a 72 mile commute (36 each way) years ago, which I did a about 3 x's per week. How doable depends on a lot of factors.

1) Your fitness to start with.

2) Road conditions. Lots of stop lights? bumpy, hilly roads? # of intersections on the commute etc.

3) Weather. Where are you? What time of year? Will it be light or dark as you make your way in or home? Wind? Rain? Thunder and lightning? Sudden summer storms are pretty unpredictable at times and you can expect to get caught out in them once or twice.

4) What you do for a living. Is it a desk job? Is it something physical you do? My job when I was doing that commute was loading trucks at a warehouse. I was exhausted sometimes on the ride home. And I worked 4 pm to midnight, often with overtime and riding home at 2 or 3 in the morning after really long days.

5) Do you have lots of responsibilities at home? Kids? Spouse? Significant other? Doesn't leave much time or energy for mowing the lawn when you get home, playing with the kids, going grocery shopping etc. You're on the bike cycling 6 hours per day and if you include in that the prep time for the ride and the shower and change of clothes it's closer to 8.

When I did I ended up sometimes getting a ride part way home with someone else who worked there to shorten the mileage. And actually had to pull off and fell asleep by the side of road one night I was so tired.

Just know that if you really want to do that kind of mileage and work a full day it will require commitment, discipline and lots of energy. You'll have to eat really well and get plenty of sleep or you'll suffer physically rather than get more fit.

All that said, I say go for it if you're so inclined. But, whew!, that's a challenge.