My Son is Naughty

Untitled from Team 5 PES on Vimeo.
My Son is Naughty
Jack and Ray were at the rugby. Ray’s team was winning
so Jack decided to give Ray a problem to deflate his ego a
bit. So Jack said “Did you know that today is my three
sons’ birthday?” “How old are they?” Ray asked taking
the bite. “I’ll give you a hint. The product of their ages is
36 and the sum of their ages is 13,” Jack replied. “That’s
no help,” said Ray. So Jack weakened and gave him
another clue. “O.K. My youngest son is very naughty.”
“Nothing to it,” exclaimed Ray and he told Jack the
correct ages of his sons.
How did Ray figure out the correct answer and what are
Jack’s sons’ ages?