TeX source:

\text { Average velocity }=\frac{\Delta \text { position }}{\Delta \text { time }}=\frac{36 \mathrm{ft}-84 \mathrm{ft}}{2 \mathrm{~s}-1 \mathrm{~s}}=\frac{-48 \mathrm{ft}}{1 \mathrm{~s}}=-48 \mathrm{ft} / \mathrm{s}.