In: Computer Science
<Place>,
<date>.
To
The Principal,
<Institution name>,
<place of institution>.
Respected Sir,
sub: re: leave approval for 1 day.
I'm <name> pursuing <Std> with the no <reg no> requesting you to permit me leave for one day, as I've to work as a tourist guide on a part-time basis, due to the heavy work for me for the earnings.
Thanking you,
yours faithfully,
<name>.