Two sisters walk toward each other from two places 630 meters apart at the same time. The younger sister walks 60 meters per minute, and the older sister walks 80 meters per minute. How many minutes does it take for the two sisters to meet on the way?
姐妹两人同时从相距630米的两地相向而行，妹妹每分钟走60米，姐姐每分钟走80米，经过多少分钟姐妹两人在途中相遇？
<gadget id="calculator">60 + 80</gadget>
<output>140</output>

<gadget id="calculator">630 / 140</gadget>
<output>9/2 = around 4.5</output>

<result>9/2 = around 4.5</result>