|A) b alone is sufficient while a alone is not sufficient||B) a alone is sufficient while b alone is not sufficient|
|C) Both a and b are sufficient||D) Neither a nor b is sufficient|
Answer: C) Both a and b are sufficient
From both a and b, we find that Kalyan is (25 - 15) = 10 years older than his brother, who was born in 1991. So, Kalyan was born in 1981.