Machine A and machine B are each used to manufacture 550 sprockets. It takes machine A 10 hours longer to produce 550 sprockets than machine B. Machine B produces 10 percent more sprockets per hour than machine A. How many sprockets per hour does machine A produces?  Choose the correct choice:
A) 6 B) 5 C) 7 D) 8 E) 9

Rationale: "machine b : takes x hours to produce 550 sprockets machine a : takes ( x + 10 ) hours to produce 550 sprockets machine b : in 1 hour , b makes 550 / x sprockets machine a : in 1 hour , a makes 550 / ( x + 10 ) sprockets equating : 1.1 ( 550 / ( x + 10 ) ) = 550 / x 605 / ( x + 10 ) = 550 / x 605 x = 550 x + 5500 55 x = 5500 x = 100 a makes 550 / ( 110 ) = 5 sprockets per hour answer : b"
Answer: B