I am three times as old as my son, five years later I shall be two and a half times as old as my son, then my present age is

Father’s present age $=3x$  years

Five years later :-

$3x+5=\frac{5}{2}\left(x+5\right)$

$\Rightarrow 6x+10=5x+25$

$\Rightarrow x=15$  years

$\Rightarrow$  father’s age $=3\left(15\right)=45$  years