Sales = 78000 + (30*marketing expenditure) + (25*RD expenditure). What is the correct interpretation of the marketing expenditure slope coefficient? All variables are in $. O After adjusting for the effect of RD expenditure, for one dollar increase in marketing expenditure, the sales is estimated to increase by 30 units. for one dollar increase in marketing expenditure, the sales is estimated to increase by 30 units. O After adjusting for the effect of RD expenditure, for one dollar increase in marketing expenditure, the sales is estimated to increase by 30 dollars. After adjusting for the effect of RD expenditure, for one dollar increase in marketing expenditure, the sales is estimated to increase by 25 dollars. Next