8.13 Following is tabulated data that were gathered from a series of Charpy impact tests on a tempered 4140 steel alloy. (a) Plot the data as impact energy versus temperature. (b) Determine a ductile-to-brittle transition temperature as that temperature corresponding to the average of the maximum and minimum impact energies. (c) Determine a ductile-to-brittle transition temperature as that temperature at which the impact energy is 70J