To determine divisibility by 11, apply the rule: the alternating sum of the digits (4 + 5 + 7 + 0) - (x + y + 9) must be divisible by 11. This yields 16 - (x + y). Setting $16 - (x + y) = 11$ gives $x + y = 5$ which leaves a remainder of 7 when divided by 11. Thus, the correct answer is 7.