1,A=15/9+3/5+(-24/9)+2/5

     =[15/9+(-24/9)]+(3/5+2/5)

     =-1+1

     =0

2,B=-6/13+5/7+(-7/13)+9/7

     =[-6/13+(-7/13)]+(5/7+9/7)

     =-1+2

     =1

3,C=5/17+(-9/15-2/17)+2/-5

     =5/17-9/15-2/17-2/5

     =(5/17-2/17)+(-9/15-2/5)

     =3/17+(-1)

     =-14/17

4,D=[1/9+(-5/17)]-[12/17-(-1/2)]+(3/6+5/9)

      =1/9+(-5/17)-(12/17+1/2)+(3/6+5/9)

      =1/9+(-5/17)-12/17-1/2+3/6+5/9

      =[(-5/17)-12/17]+(1/9+5/9)+(-1/2+3/6)

      =-1+2/3+0

      =-1/3

5,E=-5/12-[-2/8+(-3/4)+7/12]

     =-5/12+2/8-(-3/4)-7/12

     =-5/12+2/8+3/4-7/12

     =(-5/12-7/12)+(2/8+3/4)

     =-1+1

     =0

6,F=(5/16-7/13)-[-3/16-(-6/13)]

     =5/16-7/13-(-3/16+6/13)

     =5/16-7/13+3/16-6/13

     =(5/16+3/16)+(-7/13-6/13)

     =1/2+(-1)

     =-1/2

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