Mr. X aged 35 was born in January 1980 on a Monday
So the current year is 1980 + 35 = 2015
He has a son and daughter where the son is elder and the sum of the ages of his kids is 8
The possible combination of their ages is [7, 1], [ 6, 2], [5, 3]
Then son's birth year may be 2015 - 7 = 2008, 2015 - 6 = 2009, 2015 - 5 = 2010
Since son was born on X's birthday , the birth year of son is similar year of 1980
So find the similar year of 1980
Since 1980 is a leap year and the only leap year in the option is 2008
So the year of birth of the son = 2008
