Diffie-Hellman Application
Eve shouldn't be able to find the shared secret easily from the messages Alice and Bob send.

In the questions 1 and 2, you said that the shared secret is the sum/the product of the two messages, but anyone can compute them. Therefore, you are wrong.
The shared secret should be: 
1) $B=(128)(65)2 = (65)(128)2\mod p$, 
2) $B=(2^{(65)})^{(128)}=(2^{(128)})^{(65)}\mod p$.

Once you understood these two examples, I am sure you will be able to solve the 2 other questions easily by thinking a bit more about it.

Edit: you're right about 2).