First add all the (x)s together on one side of the equation. So 3x +4x is 7x
Now the problem becomes 7x -4 = 24 or -4 +7x = 24
Either way is fine.
7x -4 = 24 you need to get the x alone on one side away from the number -4 so you add 4 to each side of the = sign.
If you add +4 to -4 you get 0 so the 4 goes away, but you can't add 4 to one side unless you add 4 to the other so the problem becomes:
7x = 28 (because you added the 4 to the left side of the = sign and the right side of the = sign)
7x = 28 (now to take the 7 off of the x, you need to do the same thing to each side, but this time you divide to make the x be by itself.) 7x divided by 7 = 1x so divide 28 by 7 too and you get 4.
Just remember what you do to one side (add, subtract, divide, etc.) to make the x alone, you need to do to whatever is on the other side.