Final answer:
Kate used the addition property of equality to solve the equation incorrectly.
Step-by-step explanation:
When solving equations, it is important to perform the same operation on both sides of the equation to maintain equality. In this case, Kate incorrectly combined like terms on the left side of the equation and simplified it to p² + 12. However, she correctly simplified the right side of the equation to 8p. The property she used was the addition property of equality, which states that you can add the same value to both sides of an equation without changing its equality.