(12/13+х) - 5/13 = 9/13
12/13 + х - 5/13 = 9/13
х = 9/13 + 5/13 - 12/13
х = 2/13
(12/13 + х) -5/13= 9/13
12/13+х= 9/13+ 5/13
12/13+х= 16/13
х= 16/13-12/13
х=4/13
(12/13+х) - 5/13 = 9/13
12/13 + х - 5/13 = 9/13
х = 9/13 + 5/13 - 12/13
х = 2/13
(12/13 + х) -5/13= 9/13
12/13+х= 9/13+ 5/13
12/13+х= 16/13
х= 16/13-12/13
х=4/13