The sum of the digits of number A is 9, and the sum of the digits of number B is 10. When number A is used as the minuend and number B is used as the subtrahend, there are two borrowings when using vertical subtraction. What is the sum of the digits of the difference between A and B?
甲数各位数字之和是9，乙数各位数字之和是10，当甲数作为被减数，乙数作为减数，用竖式作减法运算时，有两次借位．那么甲、乙两数之差的各位数字之和是多少．
<gadget id="calculator">9 - 10</gadget>
<output>-1</output>

<gadget id="calculator">9 + 9 + (-1)</gadget>
<output>17</output>

<result>17</result>