The equation "3x + 4 = y + 5" demonstrates the commutative property of addition, which states that the order of terms does not affect the result of addition. The equation "3x + 4 = y + 5" also exemplifies the symmetric property of equality, which states that if two quantities are equal, then switching the order of those quantities doesn't change their equality. So, in this case, "3x + 4 = y + 5" is equivalent to "y + 5 = 3x + 4".