Mr. Wang wants to drive to City A to pick up a document. When he goes there, he travels 72 kilometers per hour and arrives in 5 hours. When he returns, he takes 4 hours to arrive. How much more kilometers will he travel per hour?
王老师要开车去A市取一份文件，去时每小时行72千米，5小时到达，返回时要4小时达到，每小时要多行多少千米？
<gadget id="calculator">5 / 4</gadget>
<output>5/4 = around 1.25</output>

<gadget id="calculator">72 * (5/4)</gadget>
<output>90</output>

<gadget id="calculator">90 - 72</gadget>
<output>18</output>

<result>18</result>