A copper wire (temperature coefficient of resistance αcu=4.0×10−3∘C−1 at 20∘C) is to be connected in series with a carbon resistor (temperature coefficient of resistance αc=−5.0×10−4∘C−1 at 20∘C). The combination must have a resistance of 20 Ω at 20∘C and be nearly independent of temperature for small temperature changes. Calculate the resistance of the carbon resistor at 20∘C that will satisfy this condition.