Suppose the cost of importing new shoes is a normally distributed random variable. The owner of Gary's Shoes is looking at shipping prices to see the expected cost to import for their new lineup. While it has been a few years, the standard deviation for importing shoes was $138.08 when last evaluated. Based on this, how many shipping companies should Gary look at to be 90% confident that the calculated average price of importing shoes is within $25 of the true amount?