🤓 Based on our data, we think this question is relevant for Professor Hatch's class at UMASS.

Hydraulic engineers in the United States often use, as a unit of volume of water, the acre-foot, defined as the volume of water that will cover 1 acre of land to a depth of 1 ft. A severe thunderstorm dumped 2.0 in. of rain in 30 min on a town of area 26 km^{2}. What volume of water, in acre-feet, fell on the town?

This problem is asking us to convert a volume in **inches times square kilometers** to **acre-feet**.

Whenever we convert units, the first step is to figure out what our starting and ending units are. We'll place the *starting units on the left*, an equals sign and *ending units on the right*, and some *conversion factors* in between.

Also, remember that if one of the starting units has an **exponent** (like **m**^{3} or **s**^{2}), the conversion factors for that unit __also__ need to have the ** same exponent**. For example:

$\left(\frac{{s}{t}{a}{r}{t}{i}{n}{g}{}{u}{n}{i}{t}}{{s}{t}{a}{r}{t}{i}{n}{g}{}{u}{n}{i}{{t}}^{{2}}}\right)\mathbf{\times}(conversionfactor)\mathbf{\times}{({c}{o}{n}{v}{e}{r}{s}{i}{o}{n}{}{f}{a}{c}{t}{o}{r})}^{\mathbf{2}}\mathbf{=}\left(\frac{{e}{n}{d}{i}{n}{g}{}{u}{n}{i}{t}}{{e}{n}{d}{i}{n}{g}{}{u}{n}{i}{{t}}^{{2}}}\right)$

The conversion factors *must* *cancel out* the starting unit and *leave* the ending unit. So to cancel out the **starting unit** in the ** numerator**, the first conversion factor must have that

The exact opposite happens with the **starting unit** in the ** denominator**. To cancel it, the second conversion factor must have that