The equation \( 4(3+5) = 12 + 20 \) demonstrates the Distributive Property. This property states that \( a(b + c) = ab + ac \). In this case, \( 4(3+5) \) distributes the \( 4 \) to both \( 3 \) and \( 5 \), resulting in \( 4 \times 3 + 4 \times 5 \), which simplifies to \( 12 + 20 \).
So the correct response is:
Distributive Property.