Let $\displaystyle{t}=\usepackage{cmbright}\Huge\$ the time, in hours, it takes the repairman to fix one pair of shoes. Then $\displaystyle{2}{t}=\usepackage{cmbright}\Huge\$ the amount of time it takes the assistant. Their rates are $\displaystyle\frac{{1}}{{t}}\usepackage{cmbright}\Huge\$ and $\displaystyle\frac{{1}}{{{2}{t}}}\usepackage{cmbright}\Huge\$ pairs per hour.

Their combined rate is $\displaystyle\frac{{1}}{{t}}+\frac{{1}}{{{2}{t}}}=\frac{{2}}{{{2}{t}}}+\frac{{1}}{{{2}{t}}}=\frac{{3}}{{{2}{t}}}\usepackage{cmbright}\Huge\$ pairs per hour.

So $\displaystyle\frac{{3}}{{{2}{t}}}\cdot{8}={16}\usepackage{cmbright}\Huge\$ or $\displaystyle\frac{{24}}{{{2}{t}}}=\frac{{16}}{{1}}\usepackage{cmbright}\Huge\$

$\displaystyle{2}{t}\cdot\frac{{24}}{{{2}{t}}}=\frac{{16}}{{1}}\cdot{2}{t}\usepackage{cmbright}\Huge\$

Therefore, $\displaystyle{24}={32}{t}\usepackage{cmbright}\Huge\$ hour, so $\displaystyle{t}=\frac{{24}}{{32}}=\frac{{3}}{{4}}\usepackage{cmbright}\Huge\$ hour.