`a, (7/12 +3/4) : 2/9 +5/8`

`= (7/12 + 9/12) * 9/2 +5/8`

`= 4/3 *9/2 +5/8`

`= 6 +5/8`

`= 48/8 +5/8`

`= 53/8`

`b, (-6/25 +3/5) : (-4)/5 +1/4`

`= (-6/25 + 15/25) * (-5)/4 +1/4`

`= 9/25 * (-5)/4 +1/4`

`= -9/20 +1/4`

`= -9/20 + 5/20`

`= -1/5`

`c, (11/12 -5/7) : 17/42 -5/8`

`= (77/84 - 60/84) * 42/17 -5/8`

`= 17/84 * 42/17 -5/8`

`= 1/2 - 5/8`

`= 4/8 -5/8`

`= -1/8`

`d, (8/15 -7/12) : 11/18 -5/11`

`= (32/60 - 35/60) * 18/11 -5/11`

`= -1/20 * 18/11 -5/11`

`= -9/110 -5/11`

`= -9/110 - 50/110`

`= -59/110`

`e, (4/9 -5/6) : 5/30 +3/4`

`= (8/18 - 15/18) * 30/5 +3/4`

`= -7/18 * 6 +3/4`

`= -7/3 +3/4`

`= -28/12 + 9/12`

`= -19/12`

`f, (9/21 -11/14) : 17/84 +1`

`= (18/42 - 33/42) * 84/17 +1`

`= -5/14 * 84/17 +1`

`= -30/17 +1`

`= -30/17 + 17/17`

`= -13/17`