The mass, \(M\) grams, of a substance at time \(t\) years is given by
$$M = 58 \mathrm { e } ^ { - 0.33 t }$$
Find the rate at which the mass is decreasing at the instant when \(t = 4\). Give your answer correct to 2 significant figures.
The mass of a second substance is increasing exponentially. The initial mass is 42.0 grams and, 6 years later, the mass is 51.8 grams. Find the mass at a time 24 years after the initial value.