7. 5 3/4 - 3 5/6
= 23/4 - 23/6
= (69 - 46)/12
= 23/12
8. 3 2/3 - 5 5/9
= 11/3 - 50/9
= (33 - 50)/9
= (- 17)/9
9. 7 3/10 + 9 12/15
= 73/10 + 147/15
= (219 + 294)/30
= 513/30
