"Eh bien, oui"
Here's why:
* Eh bien: This is a common French expression that introduces a response, similar to "well" in English.
* Oui: This is the French word for "yes."
Other options:
* Oui, bien sûr: This is a more formal way to say "yes, of course."
* Bien sûr que oui: This is another formal way to say "yes, of course."
The best way to say "why yes" in French depends on the context and the tone you want to convey.