(5_2/21 - х)+9_3/28 = 11_11/12
5_2/21 - х = 11_11/12 - 9_3/28
5_2/21 - х = 11_77/84 - 9 _21/84
5_2/21 - х = 2_56/84
5_2/21 - х = 2_14/21
х= 5_2/21 - 2_14/21
х= 4_23/21 - 2_14/21
х= 2_9/21
(5_2/21 - х)+9_3/28 = 11_11/12
5_2/21 - х = 11_11/12 - 9_3/28
5_2/21 - х = 11_77/84 - 9 _21/84
5_2/21 - х = 2_56/84
5_2/21 - х = 2_14/21
х= 5_2/21 - 2_14/21
х= 4_23/21 - 2_14/21
х= 2_9/21