How can you undo the addition of 7 on the left side of this equation? 6x + 7 = 19

To undo addition, you must subtract. Since we're subtracting 7 from one side, we must subtract 7 from the other side as well.
6x + 7 = 19
When we subtract 7, both sides are subtracting 7 to balance the equation.
6x = 12
Divide both sides by 6.
x = 2.
Hope this helps!

Subtract 7 from both sides:
6x + 7 - 7 = 19 - 7
6x = 12 is your answer.
     *To find x, just divide both sides by 6
       6x/6 = 12/6
       x = 2

Hope this helps!