x1, x2, x3 время на каждую задачу
x1 + x2 = 374/15 мин -> x1 = 374/15 - x2
x2 + x3 = 829/45 мин
x1 + x2 + x3 = 30 мин -> 374/15 - x2 + x2 + x3 = 30 -> x3 = 450/15 - 374/15 = 76/15
x2 + x3 = 829/45 -> x2 = 829/45 - 228/45 = 601/45
x1 = 374/15 - x2 = 1122/45 - 601/45 = 521/45
x1 = 11целых 26/45 мин
x2 = 13целых 16/45 мин
x3 = 5целых 1/15 мин