arithmetic - a man is 4 times as old as his daughter today twenty years later he would be just twice as old at the time of birth of his daughter how much old must the man be - skillgun

Let the ages of daughter and man today by 'x' and '4x' years respectively.
4x + 20 = 2 (x + 20) ---> As per information
x = 10 years ==> 4x = 40 years.
At the time of birth of his daughter, man must be 40 - 10 = 30 old