7. (3 marks) Suppose that you wish to estimate the difference between mean pH measurements of rainfalls in two different locations, one in relatively unpolluted area and the other in an area subject to heavy air pollution. You want to be 95% confident that the margin of error for the difference between mean pH of rainfalls in relatively unpolluted area and mean pH of rainfalls in an area subject to heavy air pollution will not exceed 0.2 pH. At least how many rainfalls (pH measurements) must be included in each sample? Assume that the variance of pH measurements in a relatively unpolluted are is equal to 2 = 0.20, and the variance of pH measurements in an area subject to heavy pollution is equal 2 to = 0.25, and samples will be of equal size (n = n =n). It is supposed that values of pH in rainfalls are normally distributed in polluted and unpolluted areas. The minimum number of rainfalls (pH measurements) that must be included in each sample is Show your work in finding the answer to the question in the problem.