Price rises to $4 per gallon. Consumers purchase only 500 gallons of milk. The government purchases 1,000 gallons of milk to support the price at $4. Thus, a total of 1,500 gallons is produced. The loss in social welfare equals 1,000 gallons of milk at $4/gallon (equals $4,000) less the producer surplus above the old demand curve up to a price of $4 (which is $500). The loss in social welfare is $3,500.