non inverting summer op amp
Ok, so you need two circuits that can perform a multiplication by a constant, and one circuit that can add the results right? I suggest you to search on "opamp adder" for the last part.
About the first part: The multiplication of the signals A and B is basically an amplification right? So if you need to amplify a voltage, and you would like to have a voltage at the output again, you need a voltage amplifier... Hope this helps.
Mark