A stream with a flow rate of 5 m³/s is having an ultimate BOD of 30 mg/litre. A wastewater discharge of 0.20 m³/s having BOD₅ of 500 mg/litre joins the stream at a location and instantaneously gets mixed up completely. The cross-sectional area of the stream is 40 m² which remains constant. BOD exertion rate constant is 0.3 per day (logarithm base to e). The BOD (in mg/litre, round off to two decimal places) remaining at 3 km downstream from the mixing location, is _______.