E3-1 Question-Why would Boeing want to keep its cash balance as low as possible? Why doesn't the company reduce its cash balance to zero?

I have attached my homework assignment that involves financial ratios and evaluating a company based upon those financial ratios that I calculated. Can you #1 please answer the question at the top regarding Boeing, #2 verify if my financial ratio calculations down the left side of the document are accurate, if not what's the correct ration #3 assist me with the question analyzing the strength of the companies based upon the financial ratios I calculated. I've also included the questions in red and highligted some as well to help make it easier. Thank you in advance!