(a+3 4/7)-1 2/7=4 3/7
(а + 3 4/7) - 1 2/7 = 4 3/7 а + 3 4/7 = 4 3/7 + 1 2/7 а + 3 4/7 = 5 5/7 а = 5 5/7 - 3 4/7 а = 2 1/7