(5) A certain educational institute has 15 centers located at different places in a city. There are three telephone operators in each center. The manager wanted to estimate the average number of calls received per telephone per week for this institute. He decided to select four centers and the number of calls received on last week for each operator were recorded. The data collected are given in Table 02. Answer the following questions. Table 02: Number of calls received for each operator 25, 15, 3D 20, 18, 22 15.20.18 (i) What is the sampling method used in this study? Justify your answer. (ii) Estimate the average number of telephone calls received per telephone operator