High concentrations of carbon monoxide CO can cause coma and possible death. The time required for a person to reach a COHb level capable of causing a coma can be approximated by the quadratic model T=.0002x2 - .316x + 127.9, where T is the exposure time in hours necessary to reach this level and 500 s x s 800 is the amount of carbon monoxide present in the air in parts per million (ppm). a) What is the exposure time when x = 720? b) Estimate the concentration of CO necessary to produce a coma in 6 hr. What is the exposure time when x = 720? hr (Round to the nearest tenth as needed.)