"My grandson is about as many days as my son is weeks,
and my grandson is as many months as I am in years.
My grandson, my son and I together are 140 years.  Can
you tell me my age in years?"
 
 
 
 

                  THE SOLUTION
 

My answer is 84 years.

Let G = grandson's age
    S = son's age
    M = my age
The three equations I developed were
    7 G = S,  12 G = M,  and  G + S + M = 140
Solving by substitution, I got M = 84.
.
.
.