To multiply a scalar by a matrix, multiply each entry by the scalar:

$3 \begin{bmatrix} -2 & 1 \\ 0 & -5 \end{bmatrix} = \begin{bmatrix} 3(-2) & 3(1) \\ 3(0) & 3(-5) \end{bmatrix} = \begin{bmatrix} -6 & 3 \\ 0 & -15 \end{bmatrix}$