To factor the expression \(-3r - 15\), we can start by identifying the common factor in both terms.
The greatest common factor of \(-3r\) and \(-15\) is \(-3\). We can factor out \(-3\) from each term:
\[ -3r - 15 = -3(r + 5) \]
Thus, the factored expression is:
\[ -3(r + 5) \]
So, filling in the blanks:
\(-3r - 15 = [-3](r + [5])\)