1/7*(7/8)у + 1/7*7 - 3/4*(2/9)у - 3/4*17/9 = 1/12.

(1/8)у + 1 - (1/6)у - 17/12 = 1/12

(1/8-1/6)у = 1/12+17/12-1; (-1/24)у=1/2; у=1/2 : (-1/24) = -1/2*24 = -12

:)