The speed difference creates a gap that grows over time.<br><br>
[[model:questions/solutions/q10090.png]]<br><br>
&bull; Speed ratio A : B = 5 : 4, so A is faster by 1 unit per hour.<br>
&bull; After 3 hours, the gap = 3 × 1 unit = 3 units = 45 km.<br>
&bull; 1 unit = 45 ÷ 3 = 15 km/h<br>
&bull; Car A&rsquo;s speed = 5 units = 5 × 15 = 75 km/h<br><br>
Car A&rsquo;s speed is 75 km/h.<br>
Check: Car B = 4 × 15 = 60 km/h. In 3 h: A travels 225 km, B travels 180 km. Gap = 45 km. ✓<br><br>
Final Answer: 75 km/h