I converted them all to common denominators and then solved for the answer. Hope this helps you :)
2. 7/15 - 3/15 = 4/15
3. 27/48 - 20/48 = 7/48
4. 15/42- 4/42 = 11/42
5. 21/24 - 4/24 = 17/24
6. -21/30 - 8/30 = -29/30
7.(negative x negative = positive) 10/12 + 9/12=1/12
8. (negative x negative = positive) -4/6 + 3/6 = -1/6
9. 1= 6/6 ...... 6/6 + 1/6 = 7/6 or 1 and 1/6
10. 1= 4/4 ...... 4/4 - 3/4 = 1/4
11. 4= 36/9 ....... 36/9 + 8/9 = 44/9 or 4 and 1/9
12. 5= 20/4 ...... 20/4 - 1/4 = 19/4 or 4 and 3/4
