Two mating parts have critical dimensions x1 and x2 as shown below. Assume that x1 and x2 are normally distributed with means 1 and mean2 and standard deviations s1 = 0.400 and s2 = 0.17. If it is desired that the probability of a smaller clearance (i.e., x1 - x2) than 0.09 should be 0.006, what distance between the nominal dimensions of the two parts (i.e., u1 and u2) should be specified by the designer?