Answer:
r = -6
Explanation:
We presume you want to find the value of r that satisfies the equation.
Subtract 6r+13 from both sides:
(6r+7) -(6r+13) = (13 +7r) -(6r+13)
-6 = r . . . . . simplify
_____
More detailed explanation
When we look at the equation we see the only variable is r, and that terms containing it appear on both sides of the equal sign. There is only one "r" term on each side, so we don't need to do any consolidation. We observe that the term with the smallest coefficient is 6r and that it is on the left side.
When we subtract 6r from the equation we will have the remaining "r" term on the right, but we will also have a constant there that we don't want. So, we can subtract that constant as well. That is why we choose to subtract 6r+13 from the equation. Doing so leaves the constants on the left and the "r" terms on the right.
As it happens, the difference between the "r" terms is plain "r", so we're done after we finish the subtraction.
__
When considering the "r" terms, we choose to subtract the term with the smallest coefficient so that the result has a positive coefficient for "r". This helps reduce mistakes in later steps, if there are any later steps.
___
Alternate "steps"
For a linear equation like this one, you can subtract one side from both sides. This might look like ...
0 = 6+r . . . . . after subtracting 6r+7 (left side) from both sides
Then you can divide by the coefficient of r (which does nothing to this equation), and subtract the resulting constant (on the side with the variable). Here, that would give ...
-6 = r
These three steps will work to solve any linear equation. Simplification steps may be required depending on the complexity. Again, it might be helpful, though is not essential, to subtract the side with the smallest coefficient of the variable.
___
Final note
The rules of equality say you can do anything you like to an equation, as long as you do the same thing to both sides. We can say "subtract the constant" because we are assured that you know it must be subtracted from both sides of the equation. Beware of any instruction that tells you to do something to one side of an equation and something different to the other side.