The equation \( 5x + 3 = x \cdot 5 + 3 \) is demonstrating the Commutative Property of Multiplication.
In particular, the property states that the order of multiplication does not affect the product, i.e., \( a \cdot b = b \cdot a \). Here \( 5x \) is equal to \( x \cdot 5 \), which showcases the commutative property.
Therefore, the correct response is The Commutative Property of Multiplication.