Walmart Inc said on Tuesday it has partnered with delivery service Postmates Inc in Charlotte, North Carolina, as part of the retailer's plan to expand its grocery home delivery services to 100 metro areas. Last month, Walmart said it would expand the service to reach more than 40 percent of U.S. households in its attempt to step up the fight against rival Amazon.com Inc.Walmart's online grocery delivery service, which provides customers fresh produce, meat, seafood and bakery items to their doorstep, has a fee of $9.95 and a $30 minimum order. They are planning to offer free shipping without a membership fee for most purchases of $35 or more.How will these affect the stock prices? Analyze the markets before making any investment decisions: $WMT & $AMZN