The younger sister walked to school, 10 minutes after departure, the elder brother chased the younger sister by bicycle, and caught up with the younger sister in 5 minutes. How many minutes has my sister been gone?
妹妹走着去上学，出发10分钟后，哥哥骑车去追妹妹，5分钟就追上了妹妹，这时哥哥发现忘带书包了，立刻返回，取了书包又去追妹妹，当再次追上妹妹时，妹妹已经走了多少分钟．
<gadget id="calculator">10 + 5 + 5</gadget>
<output>20</output>

<gadget id="calculator">10 + 5</gadget>
<output>15</output>

<gadget id="calculator">15 / 5</gadget>
<output>3</output>

<gadget id="calculator">3 - 1</gadget>
<output>2</output>

<gadget id="calculator">20 / 2</gadget>
<output>10</output>

<gadget id="calculator">10 + 20</gadget>
<output>30</output>

<result>30</result>