This letter has 3 paragraphs:
Paragraph1:
Greeting
A tie related to your friendship
Paragraph2
Your problem should be described honestly
Asking for some money to be lent
The amount of money should be mentioned
Paragraph3
Determine a deadline to pay off the debt
Thanking and promising for a future help
Ending:
We finish the letter by : All the best
With the best wishes
Wishing you the best