First we simplify like terms:
4x-2x+1/2-5/7=1/2-x
2x-3/14=1/2-x
Then you add x to both sides to get everything with the variables together.
3x-3/14=1/2
Finally, you add 3/14 to both sides for the same reason.
3x=10/14 (simplifies to 5/7)
Then we divide by 3 to get x alone.
x=5/21