radial and circumferencial pressure

A steel ring of outer diameter 300mm and internal diameter of 200mm is shrunked unto a solid steel shaft , the interference is arranged such that the radial pressure between the meeting surfaces will not fall bellow 300MN/m^2 while the assembly rotates in circles. If the maximum circumferencial stress on the inside of d surface of the ring is limited to 240MN/m^2. Determine the maximum speed at which the assembly can be rotated . Assuming that no relative slip occur between the shaft and the ring.