This question tests your ability to decipher a simple substitution code. We are given that 'WIDE' is coded as '8694' and 'INKS' is coded as '3917'. To find the code for 'I', we look for a letter common to both words. In this case, it is the letter 'I'.

In the code 'INKS' (3917), 'I' corresponds to the digit '3' and in the code 'WIDE' (8694) there is no 'I'. However, the code for 'INKS' is '3917', and the code for 'WIDE' is '8694'. The letter 'I' appears in both words. Looking at the code for 'INKS' (3917), the digit associated with 'I' is 3. Looking at the code for 'WIDE' (8694), we note that there's no 'I' present in WIDE, therefore, this solution method is invalid.

Let's try another approach. Notice that the letter 'I' appears in 'INKS' which is coded as '3917'. Therefore, we can determine the code for 'I' by comparing the position of 'I' in 'INKS' with its corresponding digit in '3917'. The letter 'I' is in the first position in 'INKS', and in the code '3917' the first digit is 3. However, comparing this to 'WIDE' which is coded as '8694', we see that 'I' is not present. Let's examine another approach.

We need to find a letter that appears in both words. There isn't a common letter, however the second approach suggests a letter to number mapping. Comparing 'INKS' (3917) and 'WIDE' (8694), we observe that the letter 'I' is common. In 'INKS', 'I' is coded as '3'. Therefore, the code for 'I' is 3.

However, there is an error in the question. If we assume the codes are independent letter mappings then this is unsolvable, but if we reconsider the provided answers, only the answer 3 is the right option. Considering the error in the question and comparing the options with the given codes, the code for 'I' is 3.