Op-Amp

Question 2a should simply be by application of a memorised formula.

For the other questions:

Do you have the general equation for the op-amp?

Can you determine the non-inverting input voltage with respect to the output?

Can you combine both of these in such a way as to answer the questions?

 

You *must* have an equation that defines the output voltage in terms of the gain and the difference between the inputs.

If you don't have that you can't do the latter parts of the question.

After learning that, there would have been some mathematics showing that as the gain approaches infinity, the characteristics of certain simple circuits are much reduced in complexity.

You need to go through your text and look for these.

Once you've found them, the answer should be very similar to some of the worked examples.