Data were collected on monthly sales revenues​ (in $1000s) and monthly advertising expenditures​ ($100s) for a sample of drug stores. the regression line relating revenues​ (y) to advertising expenditure​ (x) is estimated to be modifyingabove y with caret equals negative 48.3 plus 9.00 xy=−48.3+9.00x. what is the interpretation of the​ slope?