How many $4$-letter code can be formed using the first $10$ letters of the English alphabet, if no letter can be repeated?

First ten letters of the alphabet can be used i.e A,B, C,D,E, F,G,H, I,J.
Four letter code is to be formed.
$\square \square \square \square$
The first place (from left) can be filled by using any of the 10 alphabets. So, there are 10 ways to fill first place.
Since, repetition is not allowed . So, second place can be filled by remaining 9 alphabets.
So, there are 9 ways to fill second place.
Similarly, third place can be filled by remaining 8 alphabets.
And fourth place can be filled by remaining 7 alphabets.
Hence, the required number of ways in which four letter code can be formed is $10\times 9\times 8\times 7=5040$