Solution:
From the scatterplot given, the thread line can be drawn as the line of best fit that will pass through most of the points given on the graph as well as pass close to some other points.
The graph shows a restaurant's total monthly sales VS advertising cost.
Part A:
The graph showing the thread line;
Part B:
When advertising cost is eliminated means the sales made when no advert was made.
This is equivalent to the y-intercept of the graph when the advertising cost is zero.
That is the value of y when x = 0.
From the graph, the y-intercept is estimately at 18.
Therefore, the monthly sales is 18,000 when advertising cost was eliminated.