A warplane flying over the Black Sea is transmitting a message to a submarine. The frequency of the wave used for communication purposes is 10 MHz and its amplitude is 4000 V/m. The waves sent arrive perpendicular to the sea surface. The parameters for this sea water are given as er = 48, r = 1, o = 3. If the submarine's receiving system requires a minimum signal amplitude of 0.02 uV (microVolt), how many meters below sea level can the submarine's receiving antenna be located to ensure communication without interruption? (Do not use any approximate diffusion constant formula.)