Teacher Ding gave two math problems to 18 students in the mathematics interest group. There were 10 students who got the first problem right, 12 students who got the second problem right, and none of them got it right. ． How many students got both questions right?
丁老师出了两道数学题给数学兴趣小组的18名同学做，做对第一道题的有10名同学，做对第二道题的有12名同学，没有一道也没有做对的同学．两道题都做对了的同学有几名？
<gadget id="calculator">12 - 18</gadget>
<output>-6</output>

<gadget id="calculator">10 + (-6)</gadget>
<output>4</output>

<result>4</result>