You need to get all the x-values to one side and all the non-x-values to the other by stepping it through like this:
10x-8=9x+4
1. add the 8 to both sides.
10x-8=9x+4
+8 +8
10x=9x+12
2. subtract the 9x from both sides.
10x=9x+12
-9x -9x
X=12
And your final answer is X=12 !
I hope this makes sense and helps! :)