6/8у - 3/4 = 2у - 2 2/5,
6/8у - 2у = 3/4 - 2 2/5,
у*(6/8 - 16/8) = 3/4 - 12/5,
-10/8у = 15/20 - 48/20,
-10/8у = -33/20,
у = -33/20 : (-10/8),
у = 33/20 * 8/10,
у = 1 8/25,
проверка:
6/8*33/25 - 3/4 = 2*33/25 - 2 2/5,
198/200 - 3/4 = 66/25 - 12/5,
198/200 - 150/200 = 528/200 - 480/200,
48/200 = 48/200