15. The fish population, in thousands, in a lake at time t, in years, is modelled by the following function:
p(t) = {
3 + 1/12 t^2, if 0 <= t <= 6
2 + 1/18 t^2, if 6 < t <= 12
This function describes a sudden change in the population at time t = 6, due to a chemical spill.
a. Sketch the graph of p(t).
b. Evaluate lim p(t) as t->6- and lim p(t) as t->6+.
c. Determine how many fish were killed by the spill.
d. At what time did the population recover to the level before the spill?