A ship sails north for 2 hours, traveling a total of 15 miles. Then the ship turns south and travels 6 miles in an hour. If north is taken as the positive direction, what is the velocity of the ship?

7 miles per hour , 7 miles per hour , ,

–3 miles per hour , –3 miles per hour , ,

3 miles per hour , 3 miles per hour , ,

–7 miles per hour

please help!!!