Sophie:

Here we go: first always write out the equation. Always show all your work and you will make less mistakes.

3x - 4 + 4x = 24

Combine like variables and isolate any single numbers. Remember these equations are like a scale. What you do to one side, you do to the other. Always do the opposite of any operation on the left side and continue the same to the right, remember a scale or balance.

3x + 4x -4 = 24

7x -4 = 24

7x -4 + 4 = 24 + 4

7x  =  28

Isolate X

7x/7 =28/7

x = 4

THe first thing you do is figure out the parts that can be combined.  In this case you are able to add 3x and 4 x to get 7 x.

7x-4=24

Now you are able to isolate the "x" by adding 4 to each side : 7x-4+4=24+4

7x=28

The last part to figure out what x equals and to solve the equation is to divide both sides by 7:

7x/7=28/7

x=4