How to create an input field based on another filed input?

How to create an input field based on another filed input?

Hi there,

I have this custom field named 'Job Type' which has 2 options: Edicion, Proyecto.

What I need is if you choose 'Edicion' then another field appears to be filled: 'Number of slides' field, but if you choose 'Proyecto', 'Number of slides' doesn't appear.

I was trying with custom formulas but with no success, any ideas?

Thanks!