motorcycle and a truck are traveling towards each other from places A and B at the same time. The two vehicles met for the first time at point C, 20 kilometers away from point B, on the way, and then the two vehicles continued to move forward. The truck arrives at point A, and the motorcycle returns immediately after arriving at point B. The two vehicles meet for the second time at point D, which is 15 kilometers away from point A. Find the distance between A and B.
一辆摩托车和一辆卡车同时从A、B地相向而行．两车在途中距B地20千米的C处第一次相遇，然后两车继续前进．卡车到达A地，摩托车到达B地后都立即返回，两车在途中距A地15千米的D处第二次相遇．求A、B两地间的距离．
<gadget id="calculator">20 * 2</gadget>
<output>40</output>

<gadget id="calculator">15 * 2</gadget>
<output>30</output>

<gadget id="calculator">40 - 30</gadget>
<output>10</output>

<gadget id="calculator">20 + 10 + 15</gadget>
<output>45</output>

<result>45</result>