i'm a 7th grader that took pre-algebra in the sixth grade, so i know what i'm doing.
first you need to ind a common denominator, so the easyest thing to do is take 3/7 and multiply it by 3/3, you will get 9/21.
then add 9/21 and 1/21, but only the top numbers.
you will get an final answer of 10/21.