populate different text fields with same value based on single dropdown

I'm preparing a form with some custom calculations in Adobe Acrobat Pro DC and I'm fairly new to javascript, especially concerning form PDFs.

I have a single dropdown with three values (A, B, C) and six numeric fields (1, 2, 3, 4, 5, 6). The dropdown's default value is null and each field's default value is 0. When the dropdown = A, I'd like 1 and 4 to auto-populate with "25";

dropdown = B, 2 and 5 auto-populate with 20;

dropdown = C, 3 and 6 auto-populate with 15.

What kind of functions should I use to achieve this, and where do I put the script?

Thank you!