When writing a GT task 1 letter, I normally begin with a sentence to introduce the purpose of the letter.
A student asked me for help with the "purpose" sentence for the question below:
Although the overall purpose of the letter isn't stated in the question, I think we can still write a good purpose sentence. Here's an example:
Dear Sir or Madam,
I am writing to give you some feedback after the party that my company recently held at your hotel.