I was given this puzzle in school. Here goes :

Jack's great-grandfather was a mathematician.

He was x years old on 26 june in the year x^2

How old was Jack's great-grandfather when he published his book, cosmic topology,

on 26 June in the year 1973?

my guess is x =44 and the answer to the question is 37

is it correct? I was doing trial and error using calc.

what is the smart / algebraic way of solving it?