An experiment to measure the toxicity of formaldehyde yielded the data in the table below. The values show the percent, [math], of rats surviving an exposure to formaldehyde at a concentration of [math] (in parts per million, ppm) after [math] months.


(a) Estimate [math]:

(b) Estimate [math]:

(Be sure that you can give the practical meaning of these two values in terms of formaldehyde toxicity.)