Increase the vertical space in a fraction

Define a couple of commands to suit your needs:

\documentclass{article}
\usepackage{amsmath}
\usepackage[makeroom]{cancel}

\newcommand{\ufrac}[2]{\dfrac{#1}{#2\mathstrut}} % upper fraction
\newcommand{\lfrac}[2]{\dfrac{#1\mathstrut}{#2}} % lower fraction

\begin{document}

\begin{equation}
A=\left.\frac{\ufrac{80}{39}}{\cancel{s}\biggl(s+\lfrac{17}{39}\biggr)}\cancel{s}\,
  \right\vert_{s=0}
 =\left.\frac{\ufrac{80}{39}}{s+\lfrac{17}{39}}\right\vert_{s=0}
 =\frac{\ufrac{80}{39}}{\lfrac{17}{39}}
 =\dfrac{80}{\cancel{39}}\times \dfrac{\cancel{39}}{17}=\dfrac{80}{17}
\end{equation}
\end{document}