Forensics involving natural log

 $h=-3.9\cdot\ln\left(\frac{T-T_R}{T_O-T_R}\right)$  T is the body temperature when it was found,  $T_R$  is the (constant) temperature of the room,  $T_O$  is the body temperature at the time of death ( $T_O$  = $98.6\degree F$  ), and h is the number of hours since death.  If the body was discovered at 9am with a temperature of  $86.2\degree F$  , in a room at  $73\degree F$  , at approximately what time did the person expire?