The difference between the present age of the father and son is 30. 5 years ago, the son age is one seventh of the father age. find their present age.

The difference between the present age of the father and son is 30 means 
F-S=30 
which we rewrite as F=S+30 


5 years ago, the son age is one seventh of the father age means 
7(S-5)=F-5 
which we rewrite as F=7S-30 

Now we can write 
S+30 = 7S-30 
6S =60 
S=10 
and so F=S+30=10+30=40 

Sons is 10 and father is 40 



:)