5/7+1/9+8/9=5/7+(1/9+8/9)=5/7+1=12/7 11/4-7/11-4/11=11/4-(7/11+4/11)=11/4-1=7/4 3-5/8+5/8=3+(5/8-5/8)=3 6-1/5-1/5=6-(1/5+1/5)=6-2/5=28/5