The three-digit number 2a3 is added to 326 to get 5b9. If 5b9 is a multiple of 9, then a+b=how much.
三位数2a3加326得5b9，如果5b9是9的倍数，则a+b=多少．
<gadget id="calculator">2 + 4</gadget>
<output>6</output>

<result>6</result>