Chris, to solve these types of equations, you need to get all of the r-terms on one side, and all of the constant terms on the other side of the equals sign.
6r + 7 = 13 + 7r Subtract 6r from both sides. This will remove all of the r-terms from the left side.
7 = 13 + 7r - 6r
7 = 13 + r Now, subtract 13 from both sides. That will leave only r on the right side and the result will be:
7 - 13 = - 6 = r
