б) а = 4 5/6 - 2 1/3 = 4 5/6 - 2 2/6 = (4 - 2) + (5/6 - 2/6) = 2 + 3/6 = 2 1/2
с = 6 + 4/5 = 6 4/5
Ответ: а = 2 1/2; с = 6 4/5