How do you do this? ? explain it well !

2x-3+x=12-x+1
2x-3+x-(12-x+1)=0
2x+x-(-1x+13)-3=0
3x-(-1x+13)-3=0
3x+1x-13-3=0
4x-16=0
4x=16
x=16/4
x=4

2x-3+x=12-x+1
to solve an equation like this we have to put all the variables on one side and all the numbers on the other. we do this by subtracting, adding, multiplying, or dividing by the same things on each side of the equality.
lets add 3 to both sides first. you get
2x+x=12-x+1+3
now add x on both sides
2x+x+x=12+1+3
combine the terms
4x=16
divide by 5 on each side
x=4