An express train and a slow train respectively travel towards each other from Nanjing and Yangzhou at the same time, and after 8 hours, they meet at a distance of 30 kilometers from the midpoint. It is known that the express train travels an average of 75 kilometers per hour, how many kilometers per hour does the slow train travel on average?
一辆快车和一辆慢车分别从南京和扬州两地同时相向而行，经过8小时后在离中点30千米处相遇．已知快车平均每小时行75千米，慢车平均每小时行多少千米？
<gadget id="calculator">30 + 30</gadget>
<output>60</output>

<gadget id="calculator">60 / 8</gadget>
<output>15/2 = around 7.5</output>

<gadget id="calculator">75 - (15/2)</gadget>
<output>135/2 = around 67.5</output>

<result>135/2 = around 67.5</result>