Question 840903
let m = man's present age
let s = son's present age
:
 the age of a man ten years ago was 35 years more than the twice the age of his son.
m - 10 = 2(s-10) + 35
m - 10 = 2s - 20 + 35
m - 10 = 2s + 15
m = 2s + 15 + 10 
m = 2s + 25
:
 After how many years from now will the man's age become twice his son's age?
let y = no. of years for this to be true
m + y = 2(s + y)
m + y = 2s + 2y
m = 2s + 2y - y 
m = 2s + y
Look at the 1st equation, for this to be true; y = 25, right?