A rainfall record contains 44 years of rainfall measurement at 10 minute intervals. The maximum rainfall amounts for intervals of 10 min and 20 min, 30 min, 40 min, 50 min, and 60 min have been calculated and ranked. The top three rainfall amounts, in millimeters, for each time increment are given in the following table. At in minutes Rank 10 20 30 40 50 60 1 9.4 18.7 26.5 28.5 30.7 34.3 2 8.4 18 23.5 26.1 28.4 34.3 3 10.7 17.5 21.9 25.2 27.6 29.9 Determine the average rainfall intensities in the following table "A-B" for a return period of 30 years. Duration (min) 10 20 30 Intensity (mm/hr) A B C A = Answer: B = Answer: 40 40 50 60 F