It was reported that last year the average price of a gallon gasoline in a city X was $3.15. This year a sample of 50 gas station had an average price of $3.10 for a gallon. We assume that the...

It was reported that  last year the average price of a gallon gasoline in a city X was $3.15. This year a  sample of 50 gas station had an average price of $3.10 for a gallon. We assume that the population standard deviation of prices is $0.15. We are interested in determining whether this year mean price is less than last year. Perform a hypothesis test at the level  of significance α=0.05.