A complete mix of an activated sludge system without primary clarification is used for treatment of municipal wastewater with a flowrate of 12 MGD. The plant components include four clarifiers with a diameter of 80ft and a side-water depth of 14ft. The aeration basin volume is 3 million gallons, the mixed liquor suspended solid concentration of 3,000 mg/L, and the solid's residence time is 5 days. The return activated sludge flow rate is 10 MGD. The effluent suspended solids concentration is negligible. Sludge is wasted from the aeration basin. What is the return of suspended solids concentration (mg/L)