As part of the second stage of a drug trial, volunteers are given one of two dosages, in order to determine therapeutic levels. Volunteers who were given 4.5 mg had blood concentrations of 6.7 parts per million (ppm), while volunteers who were given 6 mg had blood concentrations of 9.1 ppm. Determine the equation of a line that models this data, where x is the dosage given and y is the blood concentration. b. Graph this line. c. If the desired concentration in the bloodstream is 7.5 ppm, what should be the therapeutic dosage? d. If the toxic concentration in the bloodstream is 11.8 ppm, what is the maximum safe dosage?