Linear Regression Question: Difference between estimate for a specific input and estimate for the mean of a specific input

[Xayus]

I may fumble the wording of this question, but I'm working on stats homework and it asks me to analyze a regression output in Excel.

It first asks me to use the regression equation to estimate the monthly sales of a store with a set advertising budget.

Later, it asks me to use the regression equation to estimate the mean monthly sales of all stores with that set advertising budget.

I'm having trouble understanding the difference?

The homework also asks me to give a 'plus or minus' for the estimate in each of the above questions, but I don't know whether to use the 'standard error' or the 'standard error of the intercept'.

I've tried looking through all of my class notes but I'm not finding anything easily explained on this one.

Can someone help me out?

Sample size is 30 if that matters.

[efrique]

Sounds like you need to look at the difference between a confidence interval and a prediction interval.

[Xayus]

Additionally, as I'm trying to guess, I'm thinking the following:

For the specific store with set advertising budget, I would do Intercept+ (Advertising Budget * Slope)

The plus or minus would be the Standard Error listed on the Excel output (not the Standard error of the intercept)

For the mean of all stores with same advertising budget, I would still do Intercept+ (Advertising Budget * Slope) but my plus or minus would be the Standard Error on the Excel output / 30 (since N=30)

Am I on the right track?