Answer:
0
Step-by-step explanation:
A NOR gate gives you the inverted output of an OR function. In numerical terms, the OR function gives you the maximum of the inputs:
A+B+C = max(A, B, C) = max(1, 1, 1) = 1
Then the output of the NOR function is its inverse:
(A+B+C)' = (1 -max(A, B, C)) = 1 -1 = 0
The output value is 0.