Answer:Step-by-step explanation:1. Contaminated Water Cleaning ProcessTo determine the concentration of pollutants over time, we use an exponential decay model. The initial concentration is 5 mg/L, and it decreases by 10% each hour. This means that each hour, 90% of the pollutant remains.Let C(t) be the concentration of pollutants in mg/L after t hours.The function is:C(t)=5(0.90)t 2. Rainfall During Typhoon AmboThis situation requires a piecewise function because the rate of rainfall changes over different time intervals.Let R(t) be the total amount of rainfall in mm after t hours.For the first three hours (0 ≤ t ≤ 3): The rain fell at a constant rate of 25 mm per hour.R(t)=25tFor the next hour (3 < t ≤ 4): The typhoon slowed down, meaning no additional rain fell during this hour. The amount of rain accumulated up to t=3 hours is 25×3=75 mm. So, for this hour, the rainfall remains constant at 75 mm.R(t)=75For the next two hours (4 < t ≤ 6): The rain started again at a constant rate of 20 mm per hour. We need to add this new accumulation to the 75 mm already accumulated. The time elapsed in this phase is (t−4) hours.R(t)=75+20(t−4)Combining these, the piecewise function is:R(t)= ⎧25t if 0≤t≤3⎨75 if 3<t≤4⎩75+20(t−4) if 4<t≤6