When you multiply your 3 digit # by 80 & 250 you have twice your original number with 4 zeros behind it. When you add 1 before you multiply by 250, then subtract 250 you negate that action. When you add twice your 4 digit # you fill the last 4 zeros with a number twice the 4 digit #. Now when you devide by 2 there is your phone number.