If the three-digit number \overline{2a3} plus \overline{326} is equal to another three-digit number \overline{5b9}, if \overline{5b9} is divisible by 9, then what is the value of a+b.
若三位数\overline{2a3}加上\overline{326}等于另一个三位数\overline{5b9}，若\overline{5b9}能被9整除，则a+b的值是多少．
<gadget id="calculator">2 + 4</gadget>
<output>6</output>

<result>6</result>