Decode the functional arithmetic operators hidden between digits, given that 561 = 9, 3713 = 6 and 4212 = 3. Evaluate and find the value of 8777.

Let the hidden operation be the sum of differences between alternate digits. $561 = (5-6) + (6-1) = -1 + 5 = 4$ → not matching Try another pattern: $(5 - 6) \times 1 + (6 - 1) \times 2 = ?$ → fails The common logic is: sum of digits of (first + last) = 5 + 1 = 6 → middle = 6 → then output = 9. By same pattern, $8777 = 8 - 7 = 1$. $\boxed{\text{Answer: (A) 1}}$