please answer 2 and 5 thank you

2. The background concentration of ammonia (NH3) in the Mud Lake as shown in figure below was measured and determined to be 20 mg/L. Mud lake has a liquid volume of 40,000 ml. Now a freshwater stream is drained into the Mud Lake at a rate of 0.1 m/s. We assume that the Mud Lake behaves as a flow balanced CSTR and neglect the ammonia loss from other potential routes such as reactions or evaporation. Estimate the time it will take to flush 60% of the ammonia from the lake (hint: write down the mass balance equation for the lake). (20 points) Ammonia polluted lake Mud Lake * = 40,000 m Fresh water stream Q-0.1 m/s Ement- 5. If the settling velocity of a particle in water is 0.7 cm/s and the overflow rate of a horizontal flow clarifier is 0.8 cm/s, what percent of the particles are retained in the clarifier