1/3 X +7=12-2/3 X WHAT IS X ?
I'm not sure if I've understood exactly the equation you've got but if it looks like this then you solve it in the following way
what you want is to get all x:es in one side and all constants on the other. To do this we begin by subtracting 7 from both sides
now we want to get all x:es on the same side and to do that we add 2/3x to both sides