A pickle-packing plant produces and discharges a waste brine solution with a salinity of 13,000 mg/L NaCl, at a rate of 100 gal/min, discharged into a stream with a flow rate above the discharge of 1.2 MGD and a salinity of 20 mg/L. Below the discharge point is a prime sport fishing spot, and the fish are intolerant of salt concentrations of 200 mg/L.

What must the level of salt in the effluent be to reduce the level in the stream to 200 mg/L?