Create a function that takes two arguments: a father's current age f_age and his son's current age s_age. Сalculate how many years ago the father was twice as old as his son, or in how many years he will be twice as old.
age_difference(36, 7) ➞ 22
# 22 years from now, the father will be 58 years old and his son will be 29 years old.
age_difference(55, 30) ➞ 5
# 5 years ago, the father was 50 years old and his son was 25 years old.
age_difference(42, 21) ➞ 0
N/A