Your answer is correct:
Number of choices for first letter
= 26
for second letter
= 26
for first digit
= 10
for second digit
=10
for third digit
= 10
for fourth digit
= 10
Total number of possible outcomes
=26*26*10*10*10*10
= 6,760,000
In the future, if you are suggesting answers for checking, it would be beneficial if you explain how you got the answer. In maths, it's how you get the answer that counts, not just the answer.