a)
=31/23-7/32-8/23
=31/23-8/23-7/32
=23/23-7/32
=1-7/32
=25/32
b)
=38/45-8/45+17/51+3/11
=30/45+17/51+3/11
=2/3+17/51+3/11
=34/51+17/51+3/11
=51/51+3/11
=1+3/11
=14/11
c)
=1/3+12/67+13/41-79/67+28/41
=1/3+(12/67-79/67)+(13/41+28/41)
=1/3+-67/67+41/41
=1/3+(-1)+1
=1/3