5/7-(1/8+4/7)=5/7-1/8-4/7=5/7-4/7-1/8=1/7-1/8=8/56-7/56=1/56
=5/7-1/8-4/7=5/7-4/7-1/8=1/7-1/8=8/56-7/56=1/56