Thirty-eight cities were researched to determine whether they had a professional sports team, a symphony, or a children's museum. of these cities, 21 had a professional sports team, 20 had a symphony, 17 had a children's museum, 14 had a professional sports team and a symphony, 10 had a professional sports team and a children's museum, 10 had a symphony and a children's museum, and 6 had all three activities. How many of the cities surveyed had only a professional sports team?