4 5/7-(×-6 3/7)=2 6/7

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