Two cars A and B drive from East Station to West Station at the same time. Car A travels 12 kilometers longer than car B per hour. After driving for four and a half hours to reach the West Railway Station, Car A did not stop. It immediately returned from the original road and met Car B at a distance of 31.5 kilometers from the West Railway Station. How many kilometers does Car A travel per hour?
甲乙两辆汽车同时从东站开往西站．甲车每小时比乙车多行12公里．甲车行驶四个半小时到达西站后，没有停留，立即从原路返回，在距离西站31.5千米的地方和乙车相遇，甲车每小时行多少千米？
<gadget id="calculator">12 * 4.5</gadget>
<output>54</output>

<gadget id="calculator">54 - 31.5</gadget>
<output>22.5</output>

<gadget id="calculator">31.5 - 22.5</gadget>
<output>9</output>

<gadget id="calculator">54 + 9</gadget>
<output>63</output>

<gadget id="calculator">63 / 12</gadget>
<output>21/4 = around 5.25</output>

<gadget id="calculator">(21/4) - 4.5</gadget>
<output>0.75</output>

<gadget id="calculator">22.5 / 0.75</gadget>
<output>30</output>

<gadget id="calculator">30 + 12</gadget>
<output>42</output>

<result>42</result>