Average speed = Total distance &divide; Total time.<br><br>
&bull; Distance at 100 km/h for 1 h: 100 km.<br>
&bull; Distance at 120 km/h for 1 h: 120 km.<br>
&bull; Distance at 80 km/h for 1 h: 80 km.<br>
&bull; Total distance = 100 + 120 + 80 = 300 km.<br>
&bull; Total time = 3 driving hours + 1 meal hour = 4 h.<br>
&bull; Average speed = 300 &divide; 4 = 75 km/h.<br>
<br>
Final Answer: 75 km/h