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8888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888

a,1/3+3/4-5/6

=4/12+9/12-5/6

=13/12-5/6

=13/12-10/12

=1/4

b,-2/3+6/5:2/3-2/15

=-2/3+9/5-2/15

=-10/15+27/15-2/15

=17/15-2/15

=1

c,

-3/7+5/13+-4/7

=-39/91+35/91+-4/7

=-4/91+-4/7

=-4/91+-52/7

=48/91

d,12/19-8/13-12/19+5/-13+2

=12/19+(-8/13-5/-13)+2

=12/19+(-1)+2

=-7/19+2

=31/19