Having bought his new system, Fritz gets his first proper gig.  It is an open-air rock concert and the nearest houses are one kilometre away.  The local authorities have told the organiser that the volume at those houses must not exceed 80dBA.  Fritz cannot monitor the volume at the houses, but he can do so at the mix position, which is 100m from the main speakers.  Assuming that there is no wind and temperature inversion, what is the theoretical, maximum volume (in dBA) at the mix position if Fritz is to comply with the rules?