5.64 The number of bacteria colonies of a certain type in samples of polluted water has a Poisson distribution with a mean of two per cubic centimeter.

a If four 1-cubic-centimeter samples are independently selected from this water, find the probability that at least one sample will contain one or more bacteria colonies.

b How many 1-cubic-centimeter samples should be selected to have a probability of approximately 0.95 of seeing at least one bacteria colony?