To solve an algebraic equation, you have to get x by itself so that x = something. In order to get x by itself you have to manipulate the equation, making sure that whatever you do to one side, you also do to the other side to keep it true. Let's do yours...
72 + 4x = 2x + 82
Let's keep x on the left and move the other numbers over to the right side (you can do it either way though). Move 72 over to the right side by subtracting it from both sides (that cancels it on the left because 72 - 72 = 0). Then combine like terms.
72 + 4x - 72 = 2x + 82 - 72
4x = 2x + 10
Now move 2x to the left side by subtracting it from both sides then combine like terms.
4x - 2x = 10
2x = 10
Lastly... divide each side by 2 (2/2 = 1 so that cancels it on the left)
x = 10/2
x = 5