the first amc 8 was given in 1985 and it has been given annually since that time. samantha turned 12 years old the year that she took the seventh amc 8 . in what year was samantha born? i don't get it

I would start like this: which year was the seventh AMC 8??

the first was in 1985
The second: 1986
3: 1987
4: 1988
5: 1989
6: 1990
7: 1991

so seventh AMC 8 took place in 1991.
she was then 12, so we can subtract this age from 1991:

1991-12=1979

so she was born in 1979!