A lake has a steady-state pollution concentration of 50 mg/L and is being fed by a stream with flow rate 50m3/day. The volume of the lake is 1.00 x 10^7 m3, and the decay rate for the pollutant is 0.15/day. If the concentration of pollutant in the incoming stream suddenly dropped to zero (the factory releasing the pollutant had shut down), how long will it take the concnetration of pollutant in the lake to become half what it is presently? [The incoming stream is still flowing at its present rate].