To rewrite the expression \( 3x(x + 3) \) using the Distributive Property, you can distribute \( 3x \) to each term inside the parentheses:
\[ 3x(x + 3) = 3x \cdot x + 3x \cdot 3 \]
Now, simplify the expression:
\[ 3x \cdot x = 3x^2 \] \[ 3x \cdot 3 = 9x \]
Putting it all together, the expression becomes:
\[ 3x(x + 3) = 3x^2 + 9x \]
Thus, the rewritten expression is \( 3x^2 + 9x \).