The detail solution to this question is like this.

Let's Say father's age in year is Y yr.Son's age in weeks is x week which if converted to year is 7x/365yr.Now as per the question

The Father replies My son is as many weeks as my grandson is in days

so grandson's age in days is X days. which if converted to year is x/365 yr.

So 1st equation: y+7x/365+x/365 100....................(1)

Father says My grandson is as many months old as I am in years.

means grandson is y months old b'coz father is y yrs old.So equating grandson's age in days(x days) from above statement with his age in months (y month) both converted in years gives us

x/365 y/12.......................(2)

solving these two equations gives y 60 in years that is father' age.grandson is as many months old as father is in years.So grandson's age is 60 months i.e 5yrs which converted to days is 1825 days.As son's age is as many weeks as grandson's age is in days.So son's age is 1825 weeks that is converted in yrs is 1825*7/365 35yrs.

father 60yrs

son 35yrs

Grandson 5yrs