N=5
first, you have to have a common denominator, in this case 12. Since the other denominators aren't 12, you have to multiply both top and bottom to get a common denominator. In this case, the equation would be 3n/12 - 10/12 = 5/12. Add 10/12 to both sides (the 5/12's side and to itself), and you then have 3n/12 = 15/12. Divide both sides by 3/12 and you get 5.