in order to solve for x you have to set x by itself, the first step is to add common like terms for example 3x and 2x are common like terms so lets add them up to get 5x-4=8 now add 4 to both sides because the only way to get rid of a negative is with a positve, now you have 5x=12. your final step is to divide 5 to both sides because the only way to get rid of a multiplication is with a division, this will leave x by itself and your answer will be x=12/5
Hope this helps