Final answer:
To predict sales using the given linear regression model, multiply the day number by 2.48 and add to 101.32. Predicted sales are $250.12 thousand for day 60 and $324.52 thousand for day 90.
Step-by-step explanation:
The student's question is related to finding the low point in the sales of a company from the year 2000 to 2009 and predicting future sales using a polynomial function. Without the actual polynomial function provided, it's impossible to definitively answer part a). However, for answering part b) of the question about sales prediction for 2015 using a polynomial function, we would need the actual polynomial expression to perform the prediction. Instead, we can answer a similar type of question using the linear regression model û = 101.32 + 2.48x, where x is the day and û is the predicted sales in thousands of dollars.
For day 60, the predicted sales would be û = 101.32 + 2.48(60) = 101.32 + 148.8 = $250.12 thousand.
For day 90, the predicted sales would be û = 101.32 + 2.48(90) = 101.32 + 223.2 = $324.52 thousand.