There are two towns, East and West, on a road. One day, A, B, and C set off at the same time. A and B travel westward from the east town, and C travels eastward from the west town. When A and C meet, the distance between B and They are 20 kilometers away. When B and C meet, A is 30 kilometers away from them. When A arrives in West Town, C is still 20 kilometers away from East Town, so when C arrives in East Town, how many kilometers away is B from West Town?
一条路上有东、西两镇，一天，甲、乙、丙三人同时出发，甲、乙从东镇向西而行，丙从西镇向东而行，当甲与丙相遇时，乙距他们20千米，当乙与丙相遇时，甲距他们30千米．当甲到达西镇时，丙距东镇还有20千米，那么当丙到达东镇是，乙距西镇多少千米？
<gadget id="calculator">30 * 2</gadget>
<output>60</output>

<gadget id="calculator">3 + 2</gadget>
<output>5</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">30 * (2/5)</gadget>
<output>12</output>

<gadget id="calculator">20 - 12</gadget>
<output>8</output>

<gadget id="calculator">8 / 12</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">60 * (2/3)</gadget>
<output>40</output>

<gadget id="calculator">60 - 40</gadget>
<output>20</output>

<result>20</result>