(9r³ + 5r² + 11r) + (-2r³ + 9r - 8r²)

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d. The random variable is the number of years in which the temperature increased from the previous year.

Step-by-step explanation:

The random variable is the amount of years that have higher average temperatures than its previous year.

As the sample is from 5 years, the random variable can take values from 0 (where none of the years increase their average temperature from its previous year) to 4 (where every year increases the average temperature).