Average speed = Total distance &divide; Total time.<br><br>
&bull; Leg 1: 180 km at 60 km/h &rarr; 180 &divide; 60 = 3 h.<br>
&bull; Leg 2: 210 km at 70 km/h &rarr; 210 &divide; 70 = 3 h.<br>
&bull; Leg 3: 240 km at 80 km/h &rarr; 240 &divide; 80 = 3 h.<br>
&bull; Total driving time = 3 + 3 + 3 = 9 h.<br>
&bull; Total stop time = 40 min + 20 min = 60 min = 1 h.<br>
&bull; Total distance = 180 + 210 + 240 = 630 km.<br>
&bull; Total time = 9 + 1 = 10 h.<br>
&bull; Average speed = 630 &divide; 10 = 63 km/h.<br>
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Final Answer: 63 km/h