Distributive Property is your answer.
In the case of "5(x - 3)", the parenthesis cannot be simplified, because you cannot combine a number and variable. To simplify, you must distribute the outside number (5), too all terms within the parenthesis
5(x - 3) = 5(x) + 5(-3)
Simplify.
5(x) = 5x
5(-3) = -15
5x - 15 is the answer (true, it makes the equation true)
Distribute Property is your answer
~Rise Above the Ordinary, Senpai