Answer:
- Professional
- Friendly
Step-by-step explanation:
Both of those tone can be used depending on the intent of the writing.
If the purpose of the writing is to talk about serious business transaction, it would be best to use a professional tone in order to shows a high level of competence. This will increase people's trust in your capability.
If the purpose of the writing is to seek semi-casual relations (such as building a network with other people within the industry), it would be best to use a friendly tone in the writing in order to establish a social relationship.