7 12/15-(3 5/15+2 4/15)=2 1/5
3 5/15+2 4/15=5 9/15 7 12/15-5 9/15=2 3/15=2 1/5
--------------------------------------------------------------------------------------
(6 1/4-2 3/4)+3 2/4=7
6 1/4-2 3/4=25/4-11/4=14/4=3 2/4 3 2/4+3 2/4=7
-----------------------------------------------------------------------------
15 1/7-(7 5/7+2 4/7)=4 6/7
7 5/7+2 4/7=9 9/7=10 2/7 15 1/7-10 2/7=106/7-72/7=34/7=4 6/7
-----------------------------------------------------------------------------------------
(6 7/21+8 5/21)-7 16/21-4 6/21=2 11/21
6 7/21+8 5/21=14 12/21 14 12/21-7 16/21=6 17/21 6 17/21-4 6/21=2 11/21
------------------------------------------------------------------
(6 9/20+3 11/20)-4 5/6-2 5/6=2 1/3
6 9/20+3 11/20=9 20/20=10 4 5/6+2 5/6=6 10/6=7 2/3 10-7 2/3=2 1/3
-----------------------------------------------------------------------------------------------
x-4 2/3=3 2/3
x=3 2/3+4 2/3
x=7 4/3=8 1/3
-------------------------------------------------
(x-3 12/17)-8 9/17=4 10/17
x-3 12/17=4 10/17+8 9/17
x-3 12/17=13 2/17
x=13 2/17+3 12/17
x=16 15/17
-----------------------------------------