a=7/12-(5/6-8/9) b=19/57-5/24 c=1-1/2+1/4-1/8+1/16

7/12-(5/6-8/9)
=7/12-(15/18-16/18)
=7/12-(-1/18)
=21/36+2/36
=23/36

19/57-5/24
=456/1368-285/1368
=171/1368
=57/456
=19/152
=8

1-1/2+1/4-1/8+1/16
=16/16-8/16+4/16-2/16+1/16
=11/16

A=[tex] \frac{7}{12} [/tex]-([tex] \frac{5}{6} [/tex]-[tex] \frac{8}{9} [/tex])=[tex] \frac{7}{12} [/tex]-(-[tex] \frac{1}{18} [/tex]=[tex] \frac{23}{36} [/tex]

B=[tex] \frac{19}{57} [/tex]-[tex] \frac{5}{24} [/tex]=[tex] \frac{1}{8} [/tex]

C=1-[tex] \frac{1}{2} [/tex]+[tex] \frac{1}{4} [/tex]-[tex] \frac{1}{8} [/tex]+[tex] \frac{1}{16} [/tex]=[tex] \frac{1}{1} [/tex]-([tex] \frac{11}{16} [/tex]=[tex] \frac{5}{16} [/tex]