In a DEA Number formula AB123456X, what calculation should be performed to verify the last digit?

The structure of a DEA number consists of a two-letter prefix, followed by six digits, and concludes with a check digit. To verify the last digit, a specific calculation is applied that incorporates the position of the digits in the sequence.

In the formula provided, we are focused on using the digits in their proper positions within the number. The first, third, and fifth digits are added together, and then the second, fourth, and sixth digits are added, with that sum being multiplied by 2. Finally, these two results are combined, and the last digit of the total is compared to the check digit at the end of the DEA number, which is represented by 'X' in the question.

The reasoning behind the correct choice is as follows: We first sum the odd-positioned digits (1, 3, and 5). For the DEA number pattern given (123456), this translates to 1 + 3 + 5. In this case, that sum is completed by aligning with the even-positioned digits (2, 4, and 6), where we double their summation, hence 2(2 + 4 + 6).

This calculation is vital as it ensures that the final result accurately reflects