Gas prices in the state are down 3-cents compared to last week in Michigan. Drivers are now paying an average of $3.15 per gallon for regular unleaded, according to AAA. That is 82-cents more than this time last year and about a penny less than this time last month. Motorists are paying an average of $47 for a full 15 gallon tank of gasoline. The auto club is reporting Metro Detroit’s average price is $3.21 a gallon. St. Clair County pumps are right around the $3.15 mark for a gallon or regular gas.