OMAHA, Neb. (AP) — Billionaire Warren Buffett is encouraging investors to maintain their faith in America’s economy and the businesses his Berkshire Hathaway conglomerate owns. In a letter to his shareholders Saturday, Buffett hardly mentioned the coronavirus that ravaged many businesses last year, saying American business will thrive over time despite the pandemic. Instead, he kept his focus on the long-term prospects for the railroad, utility and insurance businesses and stocks that Berkshire Hathaway owns. The 90-year-old Buffett also assured investors that he has no plans to quit by joking about one of Berkshire’s longest-serving managers retiring at the “ridiculously premature” age of 103.