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 formula model T=.0002xsq - .316x +127.9, where T is the exposure time in hours necessary to reach this level and 500≤x≤800 is the amount of CO present in the air in parts per million (ppm).

What is the exposure time when x = 610?

Answer 9.6 hr I got this easy

Estimate the concentration of CO necessary to produce a coma in 6 hr.
This is the part I can’t find any help on.

Question

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 formula model T=.0002xsq - .316x +127.9, where T is the exposure time in hours necessary to reach this level and 500≤x≤800 is the amount of CO present in the air in parts per million (ppm).

What is the exposure time when x = 610? 

Answer 9.6 hr I got this easy 

Estimate the concentration of CO necessary to produce a coma in 6 hr. 
This is the part I can’t find any help on.