A book has 250 pages in total, and the number of pages a child has read (4/7) is three times the number of unread pages. How many pages has this child read?
一本书共250页，一个小朋友已读页数的(4/7)是未读页数的3倍，这个小朋友读了多少页？
<gadget id="calculator">4 / 7</gadget>
<output>4/7 = around 0.571429</output>

<gadget id="calculator">(4/7) / 3</gadget>
<output>4/21 = around 0.190476</output>

<gadget id="calculator">1 + (4/21)</gadget>
<output>25/21 = around 1.190476</output>

<gadget id="calculator">250 / (25/21)</gadget>
<output>210</output>

<result>210</result>