Chapter 5.3, Problem 3E

Let $V$ be the vector space of all $\left(2\times 3\right)$ matrices. Which of the subsets in Exercises $1\text{-}4$ are subspaces of $V$?

$W=\left\{A\text{ in }V:a_{11}-a_{12}=0,a_{12}+a_{13}=0\text{ and }{a}_{23}=0\right\}$