There are 26 letters. The number of ways that 3 letters can be chosen from 26 letters is 26 x 26 x 26 = 17576
Since 241 of them are not allowed, we have
15600 - 241 = 17335 arragements
There are 10 numbers. The number of ways that 3 numbers can be chosen from 10 letters is 10 x 10 x 10 = 1000
Total number of ways is
17335 * 1000
= 17335000
