A regression model between sales (Y in $1,000), unit price (X_1, in dollars) and television advertisement (X_2 in dollars) resulted in the following function: (the -sample size is 18) E(Y) = 7 - 3X_1 + 5X_2 The coefficient of the unit price indicates that if the unit price is increased by $1 (holding advertising constant), sales are expected to decrease by $3,000 increased by $1 (holding advertising constant), sales are expected to increase by $3 decreased by $1 (holding advertising constant), sales are expected to decrease by $3 increased by $1 (holding advertising constant), sales are expected to increase by $4,000