The surface roughness of a machined part is found to depend on the tool angle (A), which can be set to 120 or 15, cutting fluid viscocity (B), which can be either 300 units or 400 units, the feed rate (C)-10 in./min. or 15 in. /min.-and whether or not cutting fluid cooler is used (D). Surface roughness measurements are taken for the different settings of the four variables (- representing a lower value (or no) and + representing a higher value (or yes) ). Surface B C D Roughness 0.00340 + 0.00362 + III 0.00301 II + 0.00182 + 0.00280 + 0.00290 + + 0.00252 +l+l+l+l+l + + 0.00160 + I 0.00336 + 0.00344 + + 0.00308 + 0.00184 + + 0.00269 + 1 + + 0.00284 + + 0.00253 + I + + 0.00163 The following calculations must be performed by hand, showing all of the intermediate steps. (a) Identify the influential parameters that affect the surface roughness. (b) Develop a regression model using the influential parameters. (c) What value of surface roughness does your regression model predict if the tool angle is set to 13", the fluid viscosity is changed to 325 units, the feed rate is changed to 12 in./min and the cutting fluid cooler is not used