Each sample of a chemical solution has a 30% chance of containing a sodium chloride (NaCl) salt. Assume that the samples are independent with regards to the presence of that NaCl salt. Define the random variable and find the probability that in the next 18 samples, exactly two samples contains the NaCl salt. Determine the probability that at least two samples contains the NaCl salt. Determine the probability that at least two but less than four samples contains the NaCl salt.