That would be one hard code to guess. The answer is simple but the number is actually. So how many letters and numbers are there?
Well, 26 letters, and we have 10 numbers including zero. I will give you two answers.
Assuming we can repeat characters i.e. we can have T56DDD,
then each slot has 36 options to choose from.
Total combinations in that case is 36^6.
(Basically 36*36*36*36*36*36)
If we cannot repeat and each character has to be unique e.g. UNIQUE
then the first slot has 36 options. It can use any character.
The second slot can use any character except the first. Thus 35 options etc.
Total combinations = 36*35*34*33*32*31
