To solve this problem, we need to identify the pattern or rule that is being applied to transform the given numbers. Let's analyze the given transformations:

4231 is transformed to 3087:
- The first digit is reduced by 1 (4 -> 3)
- The second digit is reduced by 1 (2 -> 1)
- The third digit is reduced by 1 (3 -> 2)
- The fourth digit is increased by 1 (1 -> 2)

6243 is transformed to 4086:
- The first digit is reduced by 2 (6 -> 4)
- The second digit is reduced by 2 (2 -> 0)
- The third digit is reduced by 2 (4 -> 2)
- The fourth digit is increased by 2 (3 -> 6)

From these transformations, we can observe that the rule is to reduce each digit by a certain number and then increase the fourth digit by the same number. The number by which we need to reduce the digits can be calculated by subtracting the first digit of the original number from the corresponding digit of the transformed number.

Now, let's apply this rule to the number 7614:
- The first digit is reduced by 3 (7 -> 4)
- The second digit is reduced by 3 (6 -> 3)
- The third digit is reduced by 3 (1 -> -2)
- The fourth digit is increased by 3 (4 -> 7)

However, we encounter a problem with the third digit. It becomes negative, which is not possible. Therefore, we need to apply some additional logic to handle this situation.

We can assume that if the third digit becomes negative, we need to add 10 to it to make it positive. So, -2 + 10 = 8.

Therefore, the transformed number for 7614 will be 4387.

Now, let's check the options given:
a) 3085 - Incorrect
b) 3088 - Incorrect
c) 6174 - Incorrect
d) 7164 - Correct

Hence, the correct answer is option 'D', 7164.