The sum of the digits of number A is 13, and the sum of the digits of number B is 8. When the two numbers are added vertically, there are two carries, so what is the sum of the digits of the sum of the two numbers of A and B?
甲数各位数字之和是13，乙数各位数字之和是8，当两数用竖式相加时，有两次进位，那么甲乙两数和的各位数字之和是多少．
<gadget id="calculator">9 * 2</gadget>
<output>18</output>

<gadget id="calculator">8 - 18</gadget>
<output>-10</output>

<gadget id="calculator">13 + (-10)</gadget>
<output>3</output>

<result>3</result>