WeBWorK using host: https://webwork-ptx.aimath.org, format: simple seed: 111

An experiment to measure the toxicity of formaldehyde yielded the data in the table below. The values show the percent, $P=f(t,c)$ , of rats surviving an exposure to formaldehyde at a concentration of $c$ (in parts per million, ppm) after $t$ months.

	$t=14$	$t=16$	$t=18$	$t=20$	$t=22$	$t=24$
$c=0$	100	100	100	99	97	95
$c=2$	100	99	98	97	95	92
$c=6$	96	95	93	90	86	80
$c=15$	96	93	82	70	58	36

(a) Estimate $f_t(18,6)$ :
$f_t(18, 6)\approx$

(b) Estimate $f_c(18,6)$ :
$f_c(18, 6)\approx$

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