4/42 + (х+ 1/7 ) = 8 4/21
4/42 + х + 1/7 = 8 4/21
х= 8 4/21 - 4/42 - 1/7
х= 8 8/42 - 4/42 - 6/42
х= 7 40/42
х= 7 20/21
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4/42 + ( 7 20/21 + 1/7 ) = 8 4/21
4 /42 + ( 7 20/21 + 3/21 ) = 8 4/21
4/42 + 8 2/21 = 8 4/21
4/42 + 8 4/42 = 8 4/21
8 8/42 = 8 4/21
8 4/21 = 8 4/21
3 6/19 - (х- 2 5/57) = 3 1/3
3 18/57 - х + 2 5/57 = 3 1/3
5 23/57 - х = 3 1/3
х= 5 23/57 - 3 1/3 = 5 23/57 - 3 19/57
х= 2 4/57
=====================
3 6/19 - ( 2 4/57 - 2 5/57 ) = 3 1/3
3 6/19 - ( - 1/57 ) = 3 1/3
3 18/57 + 1/57 = 3 1/3
3 19/57 = 3 1/3
3 1/3 = 3 1/3