A company that plans to introduce a new type of herbicide wants to determine which dosage produces the best crop yield for cotton. Four fields are available for testing with each field having fairly uniform characteristics (size, moisture, fertility, etc.), although there are some differences between the fields. Each field is divided into 6 equal-sized plots, with dosages of 5, 10, 15, 20, 25 and 30 units of herbicide assigned to the plots at random. The data are shown below. Answer the following questions

HW1_herbicide Field Dosage Yield F1 5 9.7 F2 5 13 F3 5 15.6 F4 5 7.1 F1 10 19.2 F2 10 20.2 F3 10 17.7 F4 10 11.8 F1 15 8.3 F2 15 6.4 F3 15 6.1 F4 15 1.7 F1 20 6.3 F2 20 6 F3 20 4 F4 20 0.5 F1 25 6.7 F2 25 5.2 F3 25 3.1 F4 25 0.8 F1 30 5.8 F2 30 3.6 F3 30 4.1 F4 30 0.2