In the case Lee said "I noticed that on February 15, 2000, Walmart issued $1 billion in bonds with a coupon rate of 7.55 per cent. The bonds mature on February 15, 2030, around 11 years from now. I also noticed from an online source that these bonds were selling for $136.38 and yielding 3.53 percent." Assuming that (1) this bond issue is a plain bond without any special features or options, (2) the prime rate is 5.50%, (3) the 20-year risk free rate is 2.90%, what would be your best guess of Walmart's cost of debt at the time of the case?