One day two mathematicians, Igor and Pavel, meet in the street.
"How are you? How are your sons?" asks Igor. "You have three sons as I remember, don't you? But I have forgotten their ages."
"Yes, I do have three sons," replies Pavel. "The product of their ages is equal to 36." Looking around and then pointing to a nearby house, Pavel says, "The sum of their ages is equal to the number of windows in the building over there."
Igor thinks for a minute and then responds, "Listen, Pavel, I cannot find the ages of your sons."
"Oh, I am very sorry", says Pavel; "I forgot to tell you that my oldest son has red hair."
Now Igor is able to find the ages of the brothers. Can you do it?
(From The Chicken from Minsk by Yuri Chernyak & Robert Rose)