First, isolate the variable which is 3x.

You can do this by subtracting 4 from both sides of the equation.

3x+4-4=243-4

3x=239

Now, if 3x equals 239, than x must be 239 divided by 3, because we devided 3x by 3 to get to x, and you always do the same to both sides.

3x=239

3x/3=239/3

x=79 2/3