@eteokal
guys its pretty simple if you follow basic algebra rules. Multiplications and divisions go first when together in an equation the left to right rule is used. We start by combining the variables that resolve first so multiplications. and then the rest as a visual aid to help us work through the equation and find x. It will look like this; 4x+2x-9=21 so 6x-9=21. At this point comes the need to isolate the unknown variable x so the -9 is a bit of a problem. To fix that problem we need to balance the equation and make the subtraction irrelevant. To do that we add 9 to both sides so that gives us 6x-9+9=21+9. Effectively what we did here simply made the troublesome subtraction irrelevant do you see it now? This resolves as 6x=30 which simplifies things as all thats left to do is divide both sides by the coefficient which is 6 so this becomes 6x/6=30/6. 30/6=5 so x is 5. For tougher equations with more variables I would suggest verifying after, to verify you simply place the outcome instead of the x variable, it will look like this; 4x5-9+2x5=21 so 6x5-9=21.