After graduating from dental school two years ago, Dr. Ruth Lewis purchased the dental practice of a long-time dentist who was retiring. In January of this year, she had to replace the outdated autoclave equipment she inherited from the previous dentist. Now, as she is preparing her budget for next year, she is concerned about understanding how her cost for sterilizing her dental instruments has changed. She has gathered the following information from her records: Month Number of instruments used Total autoclave cost January 850 $8,705 February 750 8,000 March 920 9,238 April 950 9,710 May 1,150 10,720 June 900 9,157 July 1,050 10,515 August 975 9,686