Two people, A and B, race around a circular track. They walk opposite each other at the same time and on the same ground. After meeting each other for 6 minutes, they continue to move forward for 4 minutes. At this time, A returns to the starting point, and B is still 300 meters away from the starting point. What is the length of the circular runway in meters?
甲、乙两人绕圆形跑道竞走，他们同时、同地、相背而行，6分钟相遇后又继续前进4分钟．这时甲回到出发点，乙离出发点还差300米．这个圆形跑道的长度是多少米？
<gadget id="calculator">300 / 2</gadget>
<output>150</output>

<gadget id="calculator">150 * 6</gadget>
<output>900</output>

<result>900</result>