Why do I get none displayed when I write and then print using if statement in python that does simple computation?

Trying to write a function that calculates the ground cost of shipping a product based on its weight.

https://gist.github.com/b2f88a5fad920e95c49c1420eb74b219

I used simple if and elif statements to do this but getting NONE displayed every time.

I expected output to be 53.6 but it is showing none.