It has been decided that whole body scanning technology will be used for airport security purposes. Two types of devices are being considered at a certain airport (only one will be selected): back scatter (B) and millimeter wave (W). The selected scanning equipment is to be used for six years. The economic decision criterion at this airport is to meet or exceed a 15% annual return on its investment. Based on the data found in Table P6-48, which scanner should be selected? Use the PW method of analysis. Which rule, Section 6.2.2, did you use in your analysis?