A number being divided by a number would be the same as a number multiplied by the reciprocal of the other number.
Reciprocal: the “flip” of a fraction (ex. the reciprocal of 6/7 is 7/6)
Example:
5/6 / 1/6
= 5/6*6/1
=30/6
=5
We can apply the same to the question 1/5 / 3.
1/5 / 3
=1/5*1/3
=1/15
I hope this helps! Please comment if you have any questions.