I need help on how to do this

A small lake with volume 1000m3 has a stream flowing into it with flow rate 10m3/ day and a Toluene concentration of 1.0mg/m3. A factory discharges 5m3/ day into the lake with Toluene concentration of 10mg/m3 - they want to increase effluent to 50mg/m3. Toluene decays at a rate of 0.01 day-1. Assume steady state and completely mixed (CSTR). Suppose that water flows through the lake in 3 more like a river, and thus should be modeled as a plug flow reactor. a) If you assume the stream and factory discharge are combined when they enter the lake, what is the initial concentration and flow rate entering the lake? b) What is the residence time of the pollutant in the control volume (the lake)? c) What is the final concentration leaving the lake