starts from A and walks toward B at a constant speed; B and C start from B and walks toward A at a constant speed, and the three start at the same time. B is twice as fast as C. When A and B meet, C is 30 kilometers away from B; when A and C meet, B is 80 kilometers away from B. So, how many miles is the distance between AB and AB?
甲从A出发，匀速向B行走；乙、丙从B出发，匀速向A行走，三人同时出发．乙的速度是丙的2倍．甲、乙相遇时，丙距B地30千米；甲、丙相遇时，乙距B地80千米．那么，AB两地相距多少千米．
<gadget id="calculator">2 / 2</gadget>
<output>1</output>

<gadget id="calculator">30 * 1</gadget>
<output>30</output>

<gadget id="calculator">80 - 30</gadget>
<output>50</output>

<gadget id="calculator">30 - 50</gadget>
<output>-20</output>

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

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

<gadget id="calculator">30 * 2 * 2</gadget>
<output>120</output>

<result>120</result>