Okay so what you are trying to do is solve for the X
1. The first thing you have to do is to get rid of -3, so add 3 to -3 to make it 0. But because whatever you do to one side, you have to do to the other side, you have to add 3 to 6 as well.
2. Now you are left with 2X = 9, but in order to get X by itself, you have to divide it both sides by 2. That leaves you with X = 4.5
2X - 3 = 6
Add 3 to both sides
2X = 9
Divide by 2
X = 4.5
:)