A book has 168 pages. Xiao Ming read x pages in the first week, and 42 pages in the second week. At this time, there are 72 pages left. How many pages did Xiao Ming read in the first week?
一本书有168页，小明第一周看了x页，第二周看了42页，这时还剩下72页没有看，小明第一周看了多少页？
<gadget id="calculator">168 - 42 - 72</gadget>
<output>54</output>

<result>54</result>