Go here:
http://www.bikeforums.net/showthread...essure+formula
Also check here:
http://www.sheldonbrown.com/tires.html#pressure
Basically, the narrower the tire, the more pressure it needs. The fat tires on your mountain bike don't need as much pressure. But, don't overinflate your bicycle tires, just like you shouldn't ever overinflate the tires on your car.
35 mm wide tires like what you have on your 7100 aren't that skinny, actually; two of my bikes have 28 and 23 mm tires.
By using the calculation in the first thread linked above, a rider at my weight (~210 lbs), with 700x35 tires like your Trek has (according to
http://www.trekbikes.com/us/en/bikes...0_series/7100/ ), should be running about 65 psi rear and 60 psi front. I'd say you should recalculate with your weight, then start there and run it that way for a while. I've had success with that formula for my road bike's tires.