For Question 19, the formal letter ending is 'respectfully yours' as there is nothing personal about it, but it still gives the same respect to the receiver.
For Question 20, the formal letter, "You have recently learned about an opening for an internship at a local company that you are interested in." Because to write formally, a person must treat the letter with extreme care and ensure that every word is carefully chosen. Writing a letter to a friend doesn't require extreme precision.
