Answer:
c) lost-horse forecasting.
Explanation:
According to my research on different types of forecasting methods, I can say that based on the information provided within the question the method being used in this situation is called lost-horse forecasting. This refers to using a value as a base, then analyzing all the factors and how they can affect the base value before making a final forecast. This is what the marketing manager is doing by using the known total in 2018 as a base and adjusting for different factors before making a sales forecast for 2021.
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