Answer: It would be 0
Explanation: Because like you said it would cancel each other out because if you are going 6N to the right and then you go 6N to the left you are actually not moving at all
The tension in the string and the acceleration must be equal for both masses. (See the free body diagrams)
Answer: 0.09 m
Explanation:
Centripetal acceleration in terms of tangential speed is:

where r is the radius.
It is given that,
centripetal acceleration of the mouse, 
tangential speed , 
Radius of salami is:

Thus, the radius of the salami is 0.09 m.
I would say a. hope this helps