When a baseball thrown at 85 miles per hour is hit by a bat swung at x miles per hour, the ball travels 6x - 40 feet (This formula assumes that 50 ≤ x ≤ 90 and that the bat is 35 inches long, weighs 32 ounces, and strikes a waist-high pitch so that the plane of the swing lies at 35^∘ from the horizontal.) How fast must the bat be swung for the ball to travel 350 feet?