Final answer:
The symmetric property of equality is used to justify the statement.
Step-by-step explanation:
The property of equality used to justify the statement is the symmetric property of equality.
This property states that if a = b, then b = a.
Applying this property to the given equation, if 6 + 11 = 17, then by using the symmetric property of equality, we can say that 17 = 6 + 11.