When you have an equation, your goal is to get the letter you are solving for alone. To do this, you employ a simple rule: what you do to one side of the equals sign, you must do the other.
To isolate q in -55 + q = 7, you must add 55 to the left side. q is now alone. However, because we added 55 to the left side, we must also do it to the right! 7 + 55 = 62, so the new right side is 62. Hence, we get to this:
