A mercury-in-glass thermometer consists of a wide bulb containing 1.5 cm³ of mercury and a narrow cylindrical glass tube of inner diameter 0.5 mm into which the mercury can expand. A calibration expert is placing markings on the outside of the glass, with one marking for every kelvin. How far apart should these markings be? Volumetric thermal expansion coefficient of mercury: 1.80 × 10⁻⁴ K⁻¹.