The first sentence of "The Mysterious Stranger" showed his tone very well: "His eyes rolled upwards, until nothing but the whites were visible; his hands were clasped together, until the fingers were deeply imprinted in the flesh" When the story says that "his eyes rolled upwards, until nothing but the whites were visible", that indicates that he is very stressed and upset about something serious. Then it says "his hands were clasped together, until the fingers were deeply imprinted in the flesh", now this indicated that he is very stressed and worried about something. So the tone of the excerpt would be stressed.
https://www.google.com/amp/s/m.wikihow.com/Format-a-Letter%3famp=1
Here you have steps on how to write a formate letter