Li Qiang's family drove to Qishan Scenic Spot on National Day. When I went there, I traveled 70 kilometers per hour and took 4 hours to reach the scenic spot; when I returned, it took 1 hour longer than when I went because of traffic jams. How many kilometers per hour did Li Qiang's family travel on average when they returned?
李强一家国庆节驾车到岐山景区游玩．去时每小时行70千米，用了4小时到达景区；返回时由于堵车，比去时多用了1小时．李强一家返回时平均每小时行多少千米？
<gadget id="calculator">4 + 1</gadget>
<output>5</output>

<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">70 * (4/5)</gadget>
<output>56</output>

<result>56</result>