Afather is60 years old and his son is half his age. how old was the boy when his father was four times his age

The boy would be 10 when his father was four times his age because the boy was born when the father was 30 and now that the boy is half of 60 he's 30. By subtracting 60 from 30 that gives you the age of the father when the boy was born. So when the boy is ten that would mean the father is 40 and 40 divided by ten is four

The answer is lol i dont know