12:3,2+ ( 6-( 3 78 - 1 56 )*67 ) =

12 : 3,2 + (6 - (3 7/8 - 1 5/6) * 6/7) = 8
1) 3 7/8 - 1 5/6 = 3 21/24 - 1 20/24 = 2 1/24
2) 2 1/24 * 6/7 = 49/24 * 6/7 = 7/4 = 1 3/4
3) 6 - 1 3/4 = 5 4/4 - 1 3/4 = 4 1/4
4) 12 : 3,2 = 12 : 3 2/10 = 12 : 32/10 = 12/1 * 10/32 = 3/1 * 10/8 = 30/8 = 3 6/8 = 3 3/4
5) 3 3/4 + 4 1/4 = 7 4/4 = 8