EDIT:
My proposal with the tag is this:

\documentclass[a4paper,12pt]{article}
\usepackage{mathtools,graphicx}
\begin{document}
\[
y_t=\underset{\underset{\substack{\text{Output of firms with workers} \\ \text{on one-year old contract}}}{\rotatebox{-90}{$\xrightarrow{\makebox[1cm]{}}$}}}{\dfrac{1}{2}[P_t - w_t(t-1) + u_t]}+\underset{\underset{\substack{\text{Output of firms with workers} \\ \text{on two-year (expiring) contract}}}{\rotatebox{-90}{$\xrightarrow{\makebox[1cm]{}}$}}}{\dfrac{1}{2}[P_t-w_t(t-2)+u_t]}
\]
\end{document}
or you could use also tikz-cd, used to typeset commutative diagrams and also for other things....

\documentclass[a4paper,12pt]{article}
\usepackage{tikz-cd,mathtools}
\begin{document}
\begin{tikzcd}[column sep=-.4cm]
{y_t=\dfrac{1}{2}[P_t - w_t(t-1) + u_t]}+ \arrow[d] & {\dfrac{1}{2}[P_t-w_t(t-2)+u_t]} \arrow[d] \\
\substack{\text{Output of firms with workers} \\ \text{on one-year old contract}} & \substack{\text{Output of firms with workers} \\ \text{on two-year (expiring) contract}}
\end{tikzcd}
\end{document}
cument}