Explanation

Let the son's age be x.

Then the father's age is 5x.

In 15 years, the son's age will be x+15

the father's age will be 5x+15.

According to the problem, in 15 years the father will be twice as old as his son:

                                              5x+15 = 2(x+15)

                                                      3x = 15

                                                           x = 5

Therefore, the son is currently 5 years old. 

The father's current age is 5 times that, which is 25 years old.

SH19-8-2023