The grandfather is 24 years older than his son John. John is 35 years older than his son Antony. All three combined are 100 years old.
How old are you?

The grandfather is 64 years old,
John is 37 years old and Antony is 2 years old.

Z = grandfather
Y = John
X = Antony
Y + 24 = Z
X + 35 = Y
X + Y + Z = 100
Z = X + 59
=> X + X + 35 + X + 59 = 100
3X + 94 = 100 =>
3X = 6 => X = 2
Y = 37
Z = 61