A resistor is made on a disk, allowing current to flow radially from its center to the outside. The center of the disk is a conductor producing the current with radius 0.5 mm. The ring surrounding it is made of gold out to a radius of 1.0 mm. It is then surrounded by a mixture of silver and copper, in equal portions, to a radius of 1.5 mm. The thickness of the disk is 0.25 mm. What is the total resistance?