Best range airspeed is the lowest point on the Thrust/Drag against airspeed graph. On the power required against airspeed graph it is represented by a tangent to the curve (ie a straight line from zero touching the curve!). However you look at it it is unrelated to the tail wind or headwind. With a tail wind the range will of course be greater, but 60 kts IAS will still be the best range air speed.
Of course many factors will alter the power required, such as altitude and weight, but that is not what you are being asked in the question!