Господи, они даже 0 помечены, значит совсем просто!
67) 6 1/15 - 5 5/6 + 1 7/12 * 5 1/19 = 91/15 - 35/6 + 19/12*96/19 =
= 182/30 - 175/30 + 96/12 = 7/30 + 8 = 8 7/30 = 247/30
68) 4 1/12 - 3 7/8 + 3 11/18 : 13/18 = 49/12 - 31/8 + 65/18*18/13 =
= 98/24 - 93/34 + 65/13 = 5/24 + 5 = 5 5/24 = 125/24
69) 3 1/7 * 3/11 + 3/8 : 7/12 = 22/7*3/11 + 3/8*12/7 = 6/7 + 9/14 = 21/14 = 3/2
70) 1 4/21 : 5/7 - 2/5*5/7 = 25/21*7/5 - 2/7 = 5/3 - 2/7 = 35/21 - 6/21 = 29/21