9.9 How many three-digit numbers can be formed from the digits 1, 2, $3,4,5,6?$
9.9 Each three-digit number composed of the specified digits can be considered as an arrangement with repetitions, made up of three digits taken from the given six digits. The desired number of numbers can be found using the formula (9.2):

$\widetilde{A}_{6}^{3}=6^{3}=216$.

Answer: 216 numbers.