The length of the year on the planet Mars is exactly 697 days. If Mars has a calendar with a 12-day week, and year 0 begins on the first day of the week, what is the next year which will begin on the first day of the week?
It will have to be an even-numbered year since 697 * odd will not be evenly divisible by 12
A little trial and error shows that the next time that the year will begin on the first day of the week will be Year 12
[and every 12 years after that ]
