39. 15 volleyball teams played a round-robin tournament, where each team won exactly seven matches. How many triplets of teams are there in this tournament where each team has exactly one win against the other two?
85.39. All triples of teams can be divided into two types: those that scored one point in matches against each other, and those that scored 2, 1, and 0 points in matches against each other. If the number of triples of the first type is $-a$, and the number of triples of the second type is $-b$, then $a+b=455$. On the other hand, the number of triples in which a given team scored exactly 1 point is obviously 49; in each triple of the first type, there are three such teams, and thus each such triple is counted three times, while each triple of the second type is counted exactly once. Therefore, $3a+b=49 \cdot 15=735$. From this, we get $a=140$.