Let the son be S years old Then the mother is S+21
S+21+6 = 5(S+6) S+27 = 5S+30 -3 = 4S -3/4 = S So the son is negative three-fourths of a year old, which means he has not been born yet. Since three fourths of a year before he is born is 9 months before he is born, he is just being conceived.
Having sex with his mother. LOL
Edwin