75 sounds a huge distance, but for anyone who rides regularly it is not too difficult.
You will need to get plenty of regular riding in. If you can incorporate cycling into your everyday routine it can save you excercise time. Try commuting and shopping on your bike. Any saddle-time is useful, even if you only ride for 1/2 hr.
Make sure you get a bike of sufficient quality, not too heavy, and most importantly, that fits you well. And ride.