• Tests should not print to stdout if not necessary. Instead of printing, inputs can be presented with test headers or custom assertion messages on failure.
• Tests should be organized properly with describe and it blocks, and updated to the latest version of Node used by Codewars.
• Suggested tests for edge cases: input with nothing but vowels, inputs with only vowels, sentences with only one word, empty string (if valid).

A basic arithmetic equation as a kata? And you even give the solution in the description?

And again the usual issues:

• no random tests
• no sample tests

You could also benefit reading https://github.com/codingforeveryone/READMEs/blob/master/codewars/writing-your-own-kata.md

Duplicate:

• https://www.codewars.com/kata/converting-from-celsius-to-fahrenheit-and-vice-versa
• https://www.codewars.com/kata/temperature-converter

This one was published one week ago and was retired for being a duplicate:

• https://www.codewars.com/kata/5b5616036dc79e8598000182