Use the fact that rate equals work done over time, or $\displaystyle{r}=\frac{{W}}{{t}}\usepackage{cmbright}\Huge\$ . Henry's rate for the previous job was 200 square feet per hour. The fraction $\displaystyle\frac{{{t}}}{{{1},{500}}}\usepackage{cmbright}\Huge\$ does not express Henry's rate for the new job.