SOLUTION: A man is now 30yyears older than his daughter. 15 years ago, he twice as old as his daughter. What are the present ages of the man and his daughter?

Since it is given that the man is 30 years older than his daughter,

15 years ago he still was 30 years older than the daughter, 

and, at the same time, was twice her age.


It means that 15 years ago the daughter was 30 years old, while the man was 60 years old.


Hence, now they are 45 and 75 years old.    ANSWER

Let x be the daughter age; 

then the man's age is  (x+30) years.


Fifteen years ago the daughter was (x-15) years old, while the man was (x+30)-15 = x+15 years old.


The condition says


    2*(x-15) = x + 15,   or


    2x - 30 = x + 15

    2x - x  = 15 + 30

     x      = 45  years for the daughter,

giving the same answer.