A and B set off from A and B respectively at the same time, walk towards each other, and meet each other 6 hours later. If A starts 2 hours first, they will meet at a place 12 kilometers away from the midpoint. If B starts 2 hours first, they will meet at a place 108 kilometers beyond the midpoint. Find the speed difference of A and B.
甲、乙两人分别从A、B两地同时出发，相向而行，6小时后相遇．如果甲先出发2小时，则会在距离中点还有12千米的地方相遇．如果乙先出发2小时，则会在超过中点108千米的地方相遇．求甲乙的速度差．
<gadget id="calculator">12 * 2</gadget>
<output>24</output>

<gadget id="calculator">108 * 2</gadget>
<output>216</output>

<gadget id="calculator">24 + 216</gadget>
<output>240</output>

<gadget id="calculator">6 * 2</gadget>
<output>12</output>

<gadget id="calculator">240 / 12</gadget>
<output>20</output>

<result>20</result>