database, field, combined

Is there a plugin that would let users be able to input a question in one “field”; then input there answer into a second “field” and then have both fields combined together in a new or 3rd field.

example:

1. question: |——-field one————-|
2. answer : |——-field two————-|
3. Combined: |—–field three————-|

I would like field three to be entered automatically into a new post