At 4 p. m., the temperature started to change drastically. each hour, for three hours, the temperature decreased by 7°f. which expression best shows another way to write the product for the temperature change?

First off, because the temperature is decreasing, that means the final answer would be negative, or we can also say that there would be a -1 to be multiplied by the change. 
Each hour temperature changes by 7. The question also says that temperature keeps on changing for 3 hours. Therefore the temperature change would be by 3 7's, or 7+7+7.
Lastly, add the -1 from the beginning since it is a negative temperature change, the answer is (-1)(7+7+7).

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