An algebra problem by Rakibul Hasan Emon

The present sum of the ages of a father and his son is 125 years.

so, 10 years ago ,the sum was = $125-20$ = $105$

as, 10 years ago,sons age was =36 years, so the fathers age was = $105 -36$ = $69$ years old

so ,now the fathers age is = $69+10$ = $79$

so, 8 years from present it will be = $79+8$ = $87$ years old

let $S$ be the present age of the son and $F$ be the present age of the father

10 years ago:

$S = 36$

at present:

$S = 36 + 10 = 46$

From the problem, $S + F = 125$ , substituting $46$ for $S$ we obtain,

$46 + F = 125$

$F = 79$

8 years from the present:

$F = 79 + 8 = 87$