Stan drives into the city to buy the most recent issue of Black Panther at a comic book store. On the way there he drove
15
15​​ miles per hour. With less​ traffic on his return home, he drove
35
35​ miles per hour. If the entire travel time took him
4
4​ hours, how long did it take him to get to the comic book store? Enter your answer in hours and rounded to one decimal place if needed.