To simplify the expression \(-3(6 - 3u)\), we can distribute \(-3\) to both terms inside the parentheses:
\[ -3(6) + -3(-3u) \]
Calculating each term, we have:
\[ -3 \cdot 6 = -18 \] \[ -3 \cdot -3u = 9u \]
Putting it all together, the expression simplifies to:
\[ -18 + 9u \]
Thus, the simplified expression is:
\[ 9u - 18 \]