When and why would you want to use a one-sample mean test (either z or t) or a two-sample t-test? Create a null and alternate hypothesis for one of these issues. How would you use the results?

We use inventory for cell phones and accessories in the store I work in. Basically we order the cell phones that are popular to have on-hand in the store for immediate purchase. To be able to offer accessories for those on-hand cell phones, we order various colors and brands of accessories. We keep track of the dates arrival, as well as the prices and available Mail-in-Rebates offers. We stay in contact with corporate Verizon to stay abreast of price changes, and we use spreadsheets to keep track of our inventory and prices. If the on-hand phone or accessories get low, we order more.