3 3/5 + 4/12 = 18/5 + 4/12 = 18/5 + 1/3 = (18 * 3)/(5 * 3) + (1 * 5)/(3 * 5) = 54/15 + 5/15 = 59/15 = 3 14/15
Ответ: 3 14/15