Operational amp (Inverting)
In an ideal opamp with negative feedback, the two inputs are forced to be the same voltage. 

As written for example in The Art of Electronics: "The output attempts to do whatever is necessary to make the voltage difference between the inputs zero."

Given this rule, you can calculate the values for your dc biasing circuit. 

edit: Question a is doubtful as with switch S1 open, you can not have any gain (because you input signal is not connected).