The multilinearity property states that determinant is linear in each row separately. For rows $\mathbf{r}_1, \mathbf{r}_2, \mathbf{r}_3$, suppose $\det\begin{pmatrix} \mathbf{r}_1 \\ \mathbf{r}_2 \\ \mathbf{r}_3 \end{pmatrix} = d$. What is $\det\begin{pmatrix} \mathbf{r}_1 + 3\mathbf{r}_2 \\ \mathbf{r}_2 \\ \mathbf{r}_3 \end{pmatrix}$?