a) - 9/10 : 72/100 - ( - 6/10) : (- 105/10) =
- 9/10 * 100/72 - (- 6/10) * (- 10/105) =
- 10/8 - 2/35 =
- 350/280 - 16/280 =
- 366/280 =
- 183/140
b) (- 40/13) : 80/65 - ( - 45/14) : 135/21 =
- 40/13 * 65/80 - (- 45/14) * 21/135 =
- 5/2 - (- 3/6) =
- 5/2 + 3/6 =
- 15/6 + 3/6 =
- 12/6 =
2
