Cars A and B start from AB at the same time, meet each other in 30 minutes, and drive for another 7.5 minutes after meeting. At this time, B reaches the midpoint. When A arrives at B, B is 20 kilometers away from A. Find the distance between A and B.
甲乙两车从AB两地同时出发，30分钟相遇，相遇后又行驶7.5分钟，这时乙到中点，当甲到B地时，乙距A地20千米，求AB之间距离．
<gadget id="calculator">1 / 30</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">30 + 7.5</gadget>
<output>37.5</output>

<gadget id="calculator">37.5 * 2</gadget>
<output>75</output>

<gadget id="calculator">1 / 75</gadget>
<output>1/75 = around 0.013333</output>

<gadget id="calculator">(1/30) - (1/75)</gadget>
<output>1/50 = around 0.02</output>

<gadget id="calculator">(1/50) * 37.5</gadget>
<output>0.75</output>

<gadget id="calculator">1 - 0.75</gadget>
<output>0.25</output>

<gadget id="calculator">20 / 0.25</gadget>
<output>80</output>

<result>80</result>