21. 1/12- (-7/12)= 2/3

22. 9/20-(-7/20)=4/5

23. 8 9/10-6 1/10= 2 4/5

24. (-8 6/11)-(-2 5/11)= 7

25. (-4 5/8)-3/8= 4 1/4

24 and 25 are wrong. Watch your signs.