How to write a letter expressing your inability to attend the function for which you have been invited?

From,

S. Jones, District Judge

Location

To

P.K. Raul, Secretary,

Cultural Committee

St. Martin School

Dear Mr. Raul,

Many thanks for your invitation that you so sincerely extended to me through your letter. But I am sorry to inform you that, I am quite unable to comply with your request as I have already committed myself to similar invitation from another school before your letter has reached me.

With Thanks

S. Jones