Last August the XT chain of gasoline stations had a temporary sales promotion in effect  In the promotion , any customer who made a purchase of ten or more gallons of gasoline was entitled to a free car wash 
For the month of August , XT experienced a ten percent increase in gasoline sales as compared to sales in August the previous year so evidently the promotion was successful as a means of boosting sales
Was the money that XT earned from the increase in gasoline sales enough to offset the cost of providing free car washes during the promotion.