(i) The number of possible arrangements of the 5 cars in the car park is given by the permutation formula:

\(^{18}P_5 = \frac{18!}{(18-5)!} = \frac{18!}{13!} = 1,028,160\)

(ii) To find the probability that the 5 cars are not all next to each other, first calculate the probability that they are all next to each other. Consider the 5 cars as a single block, which can be arranged in \(5!\) ways. There are 14 possible positions for this block in the line of 18 spaces:

\(5! \times 14 = 1,680\)

The probability that the cars are all next to each other is:

\(\frac{1,680}{1,028,160} = 0.001634\)

Therefore, the probability that the cars are not all next to each other is:

\(1 - 0.001634 = 0.998\)