Final answer:
The average temperature change per hour in Chicago was -4°F, calculated by dividing the total temperature drop of -28°F over 6 hours.
Step-by-step explanation:
In Chicago, the temperature dropped from 21 degrees to -7 degrees over the course of 6 hours. To find the rational number that represents the average temperature change per hour, we calculate the total change in temperature and then divide by the number of hours.
Total change in temperature = Final temperature - Initial temperature = (-7 degrees) - (21 degrees) = -28 degrees.
Next, we find the average change per hour by dividing the total change by the duration in hours.
Average change per hour = Total change in temperature / Duration in hours = -28 degrees / 6 hours = -4°F per hour.
This means that the temperature in Chicago was dropping at an average rate of 4 degrees Fahrenheit per hour.