Distance from Town A to Town B = 150 km.<br><br>
First \( \frac{2}{5} \) of journey at 100 km/h:<br>
&bull; Distance = \( \frac{2}{5} \) &times; 150 = 60 km<br>
&bull; Time = 60 &divide; 100 = 0.6 h = 36 min<br><br>
Remaining \( \frac{3}{5} \) of journey at 75 km/h:<br>
&bull; Distance = \( \frac{3}{5} \) &times; 150 = 90 km<br>
&bull; Time = 90 &divide; 75 = 1.2 h = 72 min<br><br>
Total time = 0.6 + 1.2 = 1.8 h = 1 h 48 min.<br><br>
Final Answer: 1 h 48 min