It is known that A starts from A by bicycle and drives to B at a speed of 15km per hour. After half an hour, B starts from B by bicycle and drives to A at a speed of 20km per hour. The two of them happen to be in A. If the midpoints of two places B meet, what is the distance in km between A and B?
已知甲骑自行车从A地出发，以每小时15km的速度驶向B地，经半小时后乙骑自行车从B地出发，以每小时20km的速度驶向A地，两人恰好在A，B两地的中点相遇，那么A，B两地的距离为多少km．
<gadget id="calculator">15 + 20</gadget>
<output>35</output>

<gadget id="calculator">15 * 0.5</gadget>
<output>7.5</output>

<gadget id="calculator">7.5 / 5</gadget>
<output>1.5</output>

<gadget id="calculator">35 * 1.5</gadget>
<output>52.5</output>

<gadget id="calculator">52.5 + 7.5</gadget>
<output>60</output>

<result>60</result>