BrainTwister #123: No repeats

From New Scientist #3592, 25th April 2026 [link] [link] There are many positive whole numbers whose digits are all non-zero and different: for example 1289, 93 and 876. (a) What is the smallest three-digit number whose digits are all non-zero and different? (b) How many three-digit numbers are there whose digits are all non-zero and different? [ ]