In a test, Xiaopang answered 6 questions wrongly, Xiaoya answered 7 questions wrongly, the number of questions answered correctly by Xiao Dingding was equal to the sum of the number of questions answered correctly by Xiaopang and Xiaoya, and Xiao Dingding answered 17 questions correctly. How many questions are there in the test.
一次测验中，小胖答错了6道题，小亚答错了7道题，小丁丁答对的题的数量等于小胖和小亚答对题数量的总和，小丁丁答对了17道题，这次测验共有多少道题．
<gadget id="calculator">6 + 7 + 17</gadget>
<output>30</output>

<gadget id="calculator">30 / 2</gadget>
<output>15</output>

<result>15</result>