`[123 - (20 - 4x)] : 20 = 12`
`=> 123-(20-4x) = 12 xx 20`
`=> 123 - (20-4x) = 240`
`=> 20-4x = 124 - 240`
`=> 20-4x = -116`
`=> 4x = 20 - (-117)`
`=> 4x = 136`
`=> x = 136 : 4`
`=> x = 34`
[124-(20-4.x)]:20=12
=> 124-(20-4.x) = 20 .12
=>124-(20-4.x) = 240
=> 20-4x = 124 - 240
=> 20 - 4x = -116
=> 4x = 20 + 116= 136
=> x = 136 : 4
=> x=34
\(\left[124-\left(20-4x\right)\right]:20=12\)
\(\Leftrightarrow124-20+4x=240\)
\(\Leftrightarrow4x=136\)
\(\Leftrightarrow x=34\)
[124-(20-4.x)]:20=12
[124-(20-4.x)] =12 x 20
[124-(20-4.x)] = 240
(20-4.x) = 124 - 240
(20-4.x) = -116
4.x = 20 - (-116)
4.x = 136
x = 136 : 4
x = 34