The Chicago Public Schools will pay 6.39 percent — an extraordinary interest rate by short-term lending standards — to borrow $275 million it needs to make a mandatory payment for retiree pensions before a June 30 deadline. That’s more than four times the interest rate a typical government would pay on the same borrowing deal ... It’s yet another sign of the dire financial condition of the nation’s third-largest public school system, which for months has had a “junk” credit rating from Wall Street financial institutions. CPS officials secured the $275 million on Monday from J.P. Morgan. It’s the final...