5.6. An article in Industrial Quality Control (1956, pp. 5-8) describes an experiment to investigate the effect of the type of glass and the type of phosphor on the brightness of a television tube. The response variable is the current necessary (in microamps) to obtain a specified brightness level. The data are as follows: Phosphor Type Glass 1 2 3 280 300 290 1 290 310 285 285 295 290 230 260 220 2 235 240 225 240 235 230