If x - 7 = -13, we need to get x by itself to solve this equation. To get x by itself, we can add 7 to each side (that way x will be by itself, and only on one side of the equation).
x - 7 + 7 = -13 + 7
We can add 7 to each side without changing the quantity because we do it to BOTH sides.
x = -13 + 7
Since -13 + 7 is -6,
x = -6
