Itinerary problem: Brother and sister are studying in the same school. One day, they both left home to go to school at the same time. The elder brother walked 90 meters per minute, and the younger sister walked 60 meters per minute. I went home to pick it up, and met my sister 180 meters away from the school. How far is their home from the school?
行程问题：兄妹两人在同一所学校读书，某一天两人同时离家去上学，哥哥每分钟走90米，妹妹每分钟走60米，哥哥走到学校门口发现忘记带课本，立即沿着原路回家去取，行到离学校180米处与妹妹相遇，他们家离学校有多远？
<gadget id="calculator">90 - 60</gadget>
<output>30</output>

<gadget id="calculator">2 / 30</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">180 * (1/15)</gadget>
<output>12</output>

<gadget id="calculator">60 * 12</gadget>
<output>720</output>

<gadget id="calculator">720 + 180</gadget>
<output>900</output>

<result>900</result>