To make it a simple network calculation problem you have to assume an ideal OP with infinite input resistance and gain. Then Vout will be always controlled so that the input OP difference voltage becomes zero. This gives you the oportunity to apply a basic network calculation method of your choice.
Superposition method involves that you're supplying input voltage to +ve and -ve branche seperately. The other input is connected to zero input voltage. Zero input voltage means paralleling both resistors.