56 = a + b => a = 56-b
a/3 = 1,4 b
(56-b)/3 = 14b/10
((56-b)/3) - 14b/10 = 0
(560 - 52b) /30 =0
b = 56/3 / 26/15
b = 140/13 = 10 целых и 10/13
a = 56 - b = 588/13 = 45 целых и 3/13
проверяем a/3 =1,4 b
15 целых и 1/13 = 14/10 × 140/13 = 196/13 = 15 целых и 1/13