Xiaohua's home is 600m away from school, and she goes to school at a walking speed of 50m per minute. After 8 minutes away from home, her father finds that Xiaohua's math books are left at home. Xiaohua also found that he didn't bring the book, so he returned home to get it. How many minutes after his father left home did he meet Xiaohua?
小华家离学校600m，她以每分步行50m的速度去上学，离家8分后爸爸发现小华的数学书落在家里，骑车以小华步行3倍的速度追小华，此时小华也发现没带书，返回家中去取，爸爸离家几分后与小华相遇？
<gadget id="calculator">50 * 3</gadget>
<output>150</output>

<gadget id="calculator">150 - 50</gadget>
<output>100</output>

<gadget id="calculator">8 / 100</gadget>
<output>2/25 = around 0.08</output>

<gadget id="calculator">50 * (2/25)</gadget>
<output>4</output>

<result>4</result>