k є Z
1) 4x+(3-2x)=15
4x + 3 -2x = 15
4x - 2x = 15 - 3
2x = 12
x = 6
2) 30x = -6
x = -6 * 1/30
x = -0,2
3) -6x = -12
x = -12 * ( -1/6 )
x = 2