Correct. Using the formula $\displaystyle{r}=\frac{{W}}{{t}}\usepackage{cmbright}\Huge\$ , you can set up an equation relating the individual and joint rates of installing radios: $\displaystyle\frac{{2}}{{15}}+\frac{{1}}{{12}}+\frac{{1}}{{9.5}}=\frac{{500}}{{h}}\usepackage{cmbright}\Huge\$ .