The average score of Li Ming's three sit-ups is 40, the first two are 35 and 42 respectively, what is his third score?
李明同学三次仰卧起坐的平均成绩是40个，前两次分别是35个和42个，他第三次的成绩是多少个．
<gadget id="calculator">40 * 3</gadget>
<output>120</output>

<gadget id="calculator">120 - 35 - 42</gadget>
<output>43</output>

<result>43</result>