Suppose credit rating is the only thing that determines companies' debt interest rate. Below is the interest rate associated with each credit rating. Credit rating Interest rate 3% 3.5% 4.5% 5.5% 7.5% AAA AA A BBB BB Consider a company that is issuing a ten-year fixed-rate bond with a principal value of $1 billion today. Throughout this question, ignore the time value of money (i.e., a dollar in the future is worth the same as a dollar today). (a) (1 point) Suppose the company currently has a credit rating of AA. How much interest expense (in dollars) can it save in total over the next ten years if its credit rating become AAA?