(x-3 13/21)+2 10/21=7 2/21
(x-3 13/21)=7 2/21-2 10/21
x-3 13/21=97/21
х = 97/21+ 76/21
х = 173/21=8 5/21
----------------------------------
(8 5/21-3 13/21)+2 10/21= 7 2/21
х-3 13/21+2 10/21= 7 2/21
x - 1 3/21=7 2/21
x=7 2/21+1 3/21
x=8 5/21