Differential op amp circuit explanation
Feed back will try and make the two inputs the same.  So the inverting input is also at zero volts.  The negative voltage (CV-) is sucking 5/3k = 1.66mA from that node.  The only place that current can come from is the opamp output. You need 1.66 mA flowing through R3... and that gives 1.66V on the opamp output.  (No current can come from R5 because both sides are at zero volts... that is only true when Vin is zero.)