I'd like to calculate how long on average I've lived in a single house.
Given a person's age and the number of times they've moved house as moves, return the average number of years that they've spent living in the same house.
yearsInOneHouse(30, 1) ➞ 15
yearsInOneHouse(15, 2) ➞ 5
yearsInOneHouse(80, 0) ➞ 80