The Associative Property states that the way in which numbers are grouped in addition or multiplication does not change the result. For multiplication, this means that \( (a \cdot b) \cdot c = a \cdot (b \cdot c) \).
Looking at the provided options, the equation that demonstrates the Associative Property is:
\( 3x \cdot (4x \cdot 5) = (3x \cdot 4x) \cdot 5 \)
This equation shows that the grouping of the factors does not affect the product, which is the essence of the Associative Property of multiplication.