school held a mathematics competition, and three questions A, B, and C were presented. 110 people participated in the competition, and everyone answered at least one question correctly. It is known that 52 people answered question A correctly, and 16 people only answered question A correctly; There are 61 people who answered question B correctly, 15 people who only answered question B correctly; 63 people who answered question C correctly, and 21 people who only answered question C correctly. How many people answered all three questions correctly?
某校举行数学竞赛，共出A、B、C三道题，有110人参加竞赛，每个人都至少答对一道题，已知答对A题的有52人，只答对A题的有16人；答对B题的有61人，只答对B题的有15人；答对C题的有63人，只答对C题的有21人．三道题都答对的有多少人．
<gadget id="calculator">16 + 15 + 21</gadget>
<output>52</output>

<gadget id="calculator">110 - 52</gadget>
<output>58</output>

<gadget id="calculator">63 - 110 - 58</gadget>
<output>-105</output>

<gadget id="calculator">52 + 61 + (-105)</gadget>
<output>8</output>

<result>8</result>