Answer:
1. You can speak to your best friend in any type of way while in speaking to the prime minister you would have to speak your standard language because it would more likely be in a formal setting. 2. Just the format of both letters would be different. (3. you can write slangs and expletive words to a friend but not to a prime minister)
Explanation:
You always write to a business or a prime minister or someone ahead in a formal manner while to a friend is friendly/casual.
