8/15+1/6+7/15-3/4=8/15+7/15+1/6-3/4=1+2/12-9/12=1-7/12=5/12
8/15+1/6+7/15-3/4=(8/15+7/15)-3/4+1/6=1-3/4+1/6=1/4+1/6=3/12+2/12=5/12
8/15+1/6+7/15-3/4=(8/15+7/15)+1/6-3/4=1-3/4+1/6=1/4+1/6=3/12+2/12=5/12