what is the average VLC in a target market segment if the average purchase price is $75 per visit, the frequency of purchase is 6 times per year, the contribution margin is 10%, and the average customer defection rate is 25%. Due to better operations and service management skills, the revised continious improvement goal is set at a 20% defection rate next year and 15% 2 years from now, what are the revised VLC's over their average buying life?"