To convert her $99\mathrm{.}999\mathrm{.}9$F$$F temperature to the equivalent reading on the Celsius scale, the following calculation must be performed:

TC$=($TF$32)/1\mathrm{.}8$TC$=($TF$32)/1\mathrm{.}8$TC$=$TF$1\mathrm{.}8+32$TC$=$TF$1\mathrm{.}8+32$TC$=$TF$1\mathrm{.}832$TC$=$TF$1\mathrm{.}832$TC$=($TF$+32)1\mathrm{.}8$TC$=($TF$+32)1\mathrm{.}8$