When a bactericide is added to a nutrient broth in which bacteria are growing, the The growth rate at t= 0 hours is | bacteria per hour. bacterium population continues to grow for a while, but then stops growing and begins to decline. The size of the population at time t (hours) is b = 12" + 12't - 12 t. Find the growth rates at t= 0 hours, t=6 hours, and t = 12 hours