Machine A and machine B are each used to manufacture 770 sprockets. It takes machine A 10 hours longer to produce 770 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) 5	B) 7	C) 9	D) 10	E) 12

Rationale: "machine b : takes x hours to produce 770 sprockets machine a : takes ( x + 10 ) hours to produce 770 sprockets machine b : in 1 hour , b makes 770 / x sprockets machine a : in 1 hour , a makes 770 / ( x + 10 ) sprockets equating : 1.1 ( 770 / ( x + 10 ) ) = 770 / x 847 / ( x + 10 ) = 770 / x 847 x = 770 x + 7700 77 x = 7700 x = 100 a makes 770 / ( 110 ) = 7 sprockets per hour answer : b"
Answer: B