need help with these questions, please show all work so I can understand what is going on, thank you so much

Question 1. The pH of 20 randomly selected lakes is measured. Their average ph is 5.7.Part C. Five of the 20 lakes have a pH less than 4.5. Part Ci. Build a 95% confidence interval for the proportion of lakes that have a pH less than 4.5. Part Cii. Test whether the population proportion of pH's that are less than 4.5 differs from 0.5. Part Ciii. To be accurate to within 0.1 with 95% confidence, how many lakes should we measure