Eight people P, Q, R, S, T, U, V, and W are seated in a straight line facing north. Their ages are all different: 8, 11, 15, 17, 21, 25, 27, and 30 ye...

Eight people P, Q, R, S, T, U, V, and W are seated in a straight line facing north. Their ages are all different: 8, 11, 15, 17, 21, 25, 27, and 30 years, but not necessarily in that order. The following conditions apply:

• P sits at one extreme end of the row. There are exactly three persons between P and the person who is 11 years old.
• R sits third to the left of the person who is 17 years old. The 17-year-old is not an immediate neighbor of the 11-year-old.
• R is not 11 years old. P is not 17 years old.
• Q is 15 years old. S is not the youngest.
• R is older than P but R's age is not a perfect square.
• The number of persons between P and R is the same as the number of persons between W and the 30-year-old.
• T sits immediately to the left of the person who is 8 years old.
• Q sits third to the left of S.
• The youngest person sits at the extreme right end of the row.
• All persons to the left of W are younger than W.
• U is older than V.
• Q does not sit at the extreme left end.

Question: How many persons sit between the person who is 25 years old and the person who sits immediately to the right of U?