After graduating from dental school two years ago, Dr$.$ Betty Harris 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 In January of this year, she had to replace the outdated autoclave equipment she inherited from the previous dentist.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:

$\backslash$table$[[$Month$,$Number of instruments used,Total autoclave cost$],[$January$,850,$$$7,780$