Please write a formal letter
To
The principal
For taking leaf

Dear Student,

Such questions are made for enhancing the self creative skills and should be tried
answering on your own. Here is a sample leave application for your reference:

The Principal
XYZ School
New Delhi-110025

October 10, 2019

Respected Sir,

Subject: Application for leave

This is to bring to your kind notice that my brother's marriage is to be solemnized on the 23rd of this month.  I will not be able to attend school for 5 days as there would be a lot of guests at home and I will have to help my parents in the preparing for the wedding.

I , therefore, humbly request you to  grant me leave for 5 days from October 20-24. I shall be extremely grateful to you for the same.

Yours Sincerely,
ABC
Class VI-C

Regards,