The existing posted speed limit on a section of highway is 55 mph and studies have shown that the current 65th percentile speed in 65 mph. If the posted speed finit is to be increased to the current 85th percentile speed, what should be the increase in of a that a unive that is just adequate for the existing posted speed limit? Assume a superelevation nate of 0.08 for the existing curve and for the re-designed curve.