Find the difference, then express as a fraction in simplest form.<br><br>
&bull; 7.8 km = \( \frac{78}{10} = \frac{39}{5} \) km<br>
&bull; \( 8\frac{1}{8} = \frac{65}{8} \) km<br>
&bull; Difference: \( \frac{65}{8} - \frac{39}{5} = \frac{325}{40} - \frac{312}{40} = \frac{13}{40} \) km<br><br>
Check: 8.125 - 7.8 = 0.325 = \( \frac{13}{40} \). ✓<br><br>
Final Answer: a = 13, b = 40