Question 176617
Hence means “from now.”

Let s   =   son’s age now
Then 7 years ago, son’s age was s - 7  
Since father’s age, 7 years ago was 7 times his son’s, then father’s age then was 7(s – 7) = 7s - 49
In 3 years time, son’s and father’s ages would be their ages 7 years ago, plus 10 years
Therefore, their ages, 3 years from now, or 10 years from 7 years ago will be s – 7 + 10, or s + 3 (son’s), and 7s – 49 + 10, or 7s – 39 (father’s).

Now, since in 3 year’s time, the father’s age will be twice that of his son’s, then we have: 2(s + 3)  =  7s – 39

2s  +  6  =  7s – 39
-5s  =  - 45
s  =  9

Therefore, son is now 9 years-old.

Now, since 7 years ago, father’s age was 7 times his son’s, then 7 years ago, his son was (9 – 7) = 2, which means that the father was 7(2), or 14 years-old then. 

If father was 14 years old 7 years ago, that makes him 21 years-old now.

Checking to see if this is correct, let’s calculate their ages 3 years from now. 3 years from now, the son will we 12 (9 + 3), and the father will be 24 (21 + 3). This shows that in 3 year’s time, the father, at 24, will be twice the son’s age of 12.

Therefore, the son is now 9 years old, and the father is 21 years-old.