A graph titled Monthly Sales and Advertising Costs has Advertising Costs (1,000 dollars) on the x-axis and sales (1,000 dollars) on the y-axis. A line goes through points (6.4, 117) and (6.6, 120). The scatterplot and trend line show a positive correlation between advertising costs and sales. The slope was found using the points (6.4, 117) and (6.6, 120). What is the value of b in the equation of the trend line? y = 15x + b