1/7 divided by 3 can be written as:
1 3
---- ÷ ---- =
7 1
You need to do the reciprocal of 3 so that gives you 1/3.
1 1
---- ÷ ---- =
7 3
Then multiply numerator with numerator and denominator with denominator.
1 1 1
---- ÷ ---- = --------
7 3 21
Your final answer is 1/21.