6 1/7 - (с+2 4/7)=2 5/7
6 1/7 - с - 2 4/7=2 5/7
3 4/7 - с=2 5/7
с=3 4/7 - 2 5/7
с=6/7
6 1/7 - (6/7+2 4/7)=2 5/7
6 1/7 - 3 3/7=2 5/7
2 5/7=2 5/7
.
3 5/16+(d - 2 7/16)=9 1/16
d - 2 7/16=9 1/16 - 3 5/16
d - 2 7/16=5 12/16
d=5 12/16 + 2 7/16
d=7 19/16=8 3/16
3 5/16+8 3/16 - 2 7/16=9 1/16
11 8/16 - 2 7/16=9 1/16