Answer
$[-5x+y]$
Work Step by Step
If $A$ is an $m\times n$ matrix and $B$ is an $n\times k$ matrix,
then the product $AB$ is the $m\times k$ matrix whose $ij-$th entry is the product
$(AB)_{ij}=[a_{i1}\ a_{i2}\ a_{i3}\ \ldots\ a_{in}]\left[\begin{array}{l}
b_{1j}\\
b_{2j}\\
b_{3j}\\
\vdots\\
b_{nj}
\end{array}\right]$
$=a_{i1}b_{1j}+a_{i2}b_{2j}+a_{i3}b_{3j}+\cdots+a_{in}b_{nj}$.
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A is a 1$\times$3 matrix, B is a 3$\times$1 matrix
AB is defined and is a 1$\times$1 matrix
$AB_{11}=4(-x)-1(x)+1(y)=-5x+y$
$AB=[-5x+y]$