You isolate for x. Meaning that x remains on the left side BY ITSELF all alone, in order to do that, you must bring - 13 to the RIGHT side of the equation. When you bring -13 to the right side you have to change it’s sign, so -13 will become +13.
Step-by-step explanation: x-13=37, add 13 to both sides to eliminate "-13" on the side with the variable to get the variable by itself and whatever is behind the equal sign is the value of x
