a,(-2/5+3/7)-(4/3+12/20-11/7)
b,(4 3/4-5,8)-(5 1/3-1,25+2 1/5)
c,8/13+-19/41--5/13+-9/15+22/-41
d,12/11+7/15.9/22--8/15.9/22
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