ANSWER
Substitution property of equality
Step-by-step explanation
We want to find which property guarantees that if x = y, then:
15 = x + 2y => 15 = y + 2y
The reflexive property tells us that a number is always equal to itself, and the symmetric property tells us that regardless of the side of the equal sign that two values are, they are equal.
The addition property states that we can add the same value to both sides of the equal sign.
The substitution property states that if two values are equal, then, you are allowed to substitute each value in the place of the other.
Therefore, the only correct option is Substitution property of equality.