There is a letter about reference sales. Dear Sir: How would you like to increase the efficiency of your office staff by 10% this summer? Tests in over 80 business offices using Glux air conditioners have proved that staff efficiency in these offices increased by 10% after the Glux was installed. As the increased staff efficiency means greater profits, you will therefore get back your cost within a limited period of time. The price of the air conditioner is very competitive, 5% lower than that of similar products in the market. If you would like to spread the cost, you have two years to pay up. In addition, improvements in the new model will also make your operating costs low. Won't you call and ask us to send you our technical personnel to identify your specific needs and do the installation? Each day's delay costs you money. Yours Faithfully, Tony Smith Chief seller What is the purpose of the letter? To sale ______.