In how many ways you can form a combination of 3 numbers and 3 letters in a plate number if repetition is allowed

Your plate numbers will be like

where each is a number, and each is a letter. Assuming you can use all numbers and letters, you have 10 possible choices for every place (all the digits from 0 to 10) and 26 possible choices for every place (all the letters from a to z).

So, if you multiply all the possible choices, you have

So, there is a total of

possible plate numbers with 3 letters and 3 numbers, if repetitions are allowed.