For $A = \begin{bmatrix}2 & 5 & -1 \\ 3 & 0 & 4 \\ 6 & -2 & 1\end{bmatrix}$, what is $a_{13} + a_{21}$?

Explanation

1. 01

   $a_{13}$ is row 1, column 3: $-1$. $a_{21}$ is row 2, column 1: $3$.

2. 02

   So $a_{13} + a_{21} = -1 + 3 = 2$.