The mass (in grams) of a radioactive sample t hours after an experiment begins is modeled by the function f(t)=100e−0.05t. Which of the following is closest to f′(4), and what does this value represent?
a) f′(4)≈−0.82; the mass is decreasing at about 0.82 gram per hour at t=4 hours.
b) f′(4)≈4.1; the mass is increasing at about 4.1 grams per hour at t=4 hours.
c) f′(4)≈−4.1; the mass is decreasing at about 4.1 grams per hour at t=4 hours.
d) f′(4)≈−16.4; the mass is decreasing at about 16.4 grams per hour at t=4 hours.