Target total time = Total distance &divide; Target average speed.<br><br>
&bull; Target time = 320 &divide; 80 = 4 h.<br>
&bull; Time used so far:<br>
&bull; First 80 km at 40 km/h: 80 &divide; 40 = 2 h.<br>
&bull; Next 80 km at 80 km/h: 80 &divide; 80 = 1 h.<br>
&bull; Total time used = 2 + 1 = 3 h.<br>
&bull; Remaining time = 4 &minus; 3 = 1 h.<br>
&bull; Remaining distance = 320 &minus; 80 &minus; 80 = 160 km.<br>
&bull; Required speed = 160 &divide; 1 = 160 km/h.<br>
<br>
Final Answer: 160 km/h