SOLUTION: The age of a man is twice the sum of the ages of his two sons, and five year ago his age was thrice the sum of their ages. Find the man's present age.

Let S = the SUM of the two sons.

So the age of the man = 2S

His age five years ago was 2S-5

equals

3 times

S-10  [Why 10?  Because there are two sons and we must subtract
      [ 5 two times, once for each son. 

2S-5 = 3(S-10)

Solve that for S.  Then substitute what you get
for S in 2S to find the present age of the man.

Edwin