45/140 - х = 12/140+ 21/140
45/140 - х = 33/140
х = 45/140 - 33/140
х = 12/140
45/140 - 12/140 = 12/140 + 21/140
33/140 = 33/140
45/140 - х = 12/140+ 21/140
45/140 - х = 33/140
х = 45/140 - 33/140
х = 12/140
45/140 - 12/140 = 12/140 + 21/140
33/140 = 33/140