\( \definecolor{colordef}{RGB}{249,49,84} \definecolor{colorprop}{RGB}{18,102,241} \)
Find the matrix representing a horizontal stretch by a factor of 3.
$$ \mathbf{S} = \begin{pmatrix}\input{145089}{}{3em}{2em}{}{} & \input{245089}{}{3em}{2em}{}{}\\ \input{345089}{}{3em}{2em}{}{} & \input{445089}{}{3em}{2em}{}{}\\ \end{pmatrix}$$