United Airlines has increased its checked-baggage fees by $5. The first checked bag is now $35 each way, the second, $45. Travelers can avoid the increase by prepaying for bags in advance. The checked-bag prices remain $30 and $40 if the fee is paid at any time before online check-in. The increase takes effect for travel beginning March 6. Travelers who bought their tickets before Friday, Feb. 21 will be exempt and continue to pay $30 and $40.