Here are the matches for Column A and Column B based on the context of each letter type:
Column A | Column B
--------------------------------------------------|------------------------------------------------
Order letter | 5. Please supply us with 10 kg of fresh vector to be delivered at the end of the month.
Sales letter | 5. The special offer of buy one and get one free "is valid until the end of September.
Complaint letter | 7. The cutlery was filthy and the waiters were rude.
Adjustment letter | 4. Thank you for the opportunity but I already have another function to attend.
Inquiry letter | 3. I would like to book the Hall for a Farewell party of 50 people on the 4th December. Please let me know if it is available.
Follow up letter | 8. Thank you for the information you sent regarding the booking for the 4th of December. Please let me know if the rates are still the same as advertised on the website.
Letter of recommendation | 2. Shasha is a dedicated, hardworking student who is able to work well with others.
Acknowledgement letter | 1. I have been offered a wonderful opportunity in New Zealand and will start on the 1st of January.
Note: It appears that the number 5 is listed twice in Column B, so I assigned one from the other potential meanings based on relevance, and included both different sentences under the 'Order Letter' and 'Sales Letter'.