11. а) x + 2x = 45
3x = 45
x = 45/3
x = 15.
б) 3x + x = 14
4x = 14
x = 14/4
x = 3,5.
в) x + 2x+ 3x = 30
6x = 30
x = 30/6
x = 5.
12. а) x + (x+4) = 22
2x + 4 = 22
2x = 22-4
2x = 18
x = 18/2
x = 9.
б) (x-7) + x = 33
2x - 7 = 33
2x = 33+7
2x = 40
x = 40/2
x = 20.
в) x + (x-1) = 40
2x - 1 = 40
2x = 40+1
2x = 41
x = 41/2
x = 20,5.