How do you write an application to your head master requesting him to allow our class to participate in arts and crafts exhibition organized by the board of secondary education Karachi?

It should go something like this:

Dear sir:

Our class < Standard and section> would like to participate in the 'Arts and Crafts' exhibition being organised by the board of secondary education, Karachi.

The exhibition is to be held on <Date of exhibition> at <Venue>.

<Number of students participating> students from our class would like to attend this exhibition. The total cost to the school would be <Cost of transport, lunch etc.>. The cost can be charged on a per head basis to the children's parents.

We seek your permission in this regards.

Yours faithfully,

<Sender's name>