Final answer:
Shakerville was 11°F warmer than Cassidy City, not -11°F. The correct calculation for the difference in temperature is -6 - (-17), which simplifies to 11°F. Manny's mistake was in not correctly applying the rule for subtracting a negative number.
Step-by-step explanation:
The question asks how much warmer Shakerville was than Cassidy City. The overnight low temperature in Cassidy City was -17°F and in Shakerville it was -6°F. To find the difference in temperature, you subtract the lower temperature (from Cassidy City) from the higher temperature (from Shakerville). The correct calculation is -6 - (-17), which is the same as -6 + 17 because subtracting a negative is the same as adding its positive equivalent. So, the calculation becomes 17 - 6, which equals 11°F. Thus, Shakerville was 11°F warmer than Cassidy City. Therefore, Manny's answer of -11°F is incorrect because he did not apply the rule of subtracting a negative correctly.