Q: WHAT YEAR WAS CAINAN BORN?
A: IT DEPENDS WHAT CALENDAR YOU ARE USING!
On the Gregorian calendar (the one you might have on your wall) the year was 3721 BC.
On the Hebrew calendar, sometimes called the biblical calendar, the year was 326 AM.
Genesis 5:9 - And Enos lived ninety years, and begat Cainan