In the highly competitive world of healthcare, one business is taking a $460 million gamble on Everett. That gamble is a 12-story, 680,000-square-foot medical tower, which Providence Regional Medical Center Everett plans to open June 14. The debt for the project will take 40 years to pay off. The medical tower ranks as the most expensive construction project ever undertaken by Providence Health & Services, the Everett hospital's corporate parent. This in an organization that operates 28 hospitals in five western states and took in $8.1 billion in revenues last year. "There's certainly a huge commitment to this which brings about huge risk," said Dave Brooks, the Everett hospital's CEO.