Amodel car has a scale factor of 1/64. the diameter of a tire on the model is 0.39. so, the diameter of the tire on an actual car must be inches. (one decimal place)

24.96 inches.

This model car is having 1/64 scale which means the actual car is 64 times longer. To know the diameters of the actual car, you just need to divide the diameter of model car with the scale. If the diameter of the model is 0.39 inch then the calculation is:
Diameter of actual car x scale = diameter of model 
Diameter of actual car = diameter of model / scale = 0.39 inch / (1/64)=  24.96 inch.

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