Răspuns :
7( x + 3 ) - 3x = 5 + 6( x + 5 ) - 4x
7x + 21 - 3x = 5 + 6( x + 5 ) - 4x
7x + 21 - 3x = 5 + 6x + 30 - 4x
4x + 21 = 5 + 6x + 30 - 4x
4x + 21 = 35 + 6x - 4x
4x + 21 = 35 + 2x
4x - 21 + 21 = 35
4x - 2x = 35 - 21
2x = 35 - 21
2x = 14
x = 14 : 2
x = 7
7x + 21 - 3x = 5 + 6( x + 5 ) - 4x
7x + 21 - 3x = 5 + 6x + 30 - 4x
4x + 21 = 5 + 6x + 30 - 4x
4x + 21 = 35 + 6x - 4x
4x + 21 = 35 + 2x
4x - 21 + 21 = 35
4x - 2x = 35 - 21
2x = 35 - 21
2x = 14
x = 14 : 2
x = 7