An activated sludge system treats 1500 m3/day of raw wastewater with a BOD of 250 mg/L. The reactor volume is 375 m3. The kinetic parameters were determined to be: x = 3 day-1, Y = 0.55 kg SS/kg cells, and Ks = 150 mg/L. If the required effluent BOD is 15 mg/L, what is the mixed liquor suspended solids concentration?