a is a three-digit number, its hundreds digit is 4, a+9 is divisible by 7, a-7 is divisible by 9, what is a?
a是一个三位数，它的百位数字是4，a+9能被7整除，a-7能被9整除，问a是多少？
<gadget id="calculator">63 * 6</gadget>
<output>378</output>

<gadget id="calculator">378 + 61</gadget>
<output>439</output>

<result>439</result>