How to setup autofill for constant sum fields or piping for autofill / “must sum to” fields

Hi,
I am looking to auto fill fields in constant sum question to a total of 100.
For example in a three field constant sum question, when one filed is filled as 50, second field 30 and then third field should auto fill as 20 (see the attached picture).

Could you please help with with this functionality (JS code?)
Many thanks!