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[ 121 - 3 ( 2x - 1 ) ] . 4 ^ 5 = 4 ^ 6
[ 121 - 3 ( 2x - 1 ) ] = 4^6 : 4^5
[ 121 - 3 ( 2x - 1 ) ] = 4 ^1
[ 121 - 3 ( 2x - 1 ) ] = 4
3 ( 2x - 1 ) = 121 - 4
3 ( 2x - 1 ) = 117
2x - 1 = 117 : 3
2x -1 = 39
2 x = 39 + 1
2 x = 40
x = 40 : 2
x = 20