Solve the second equation for \(x\): \(x = y + 3\).


Let \( d \) be the distance between City A and City B.
Time from A to B = \( \frac{d}{80} \)
Time from B to A = \( \frac{d}{100} \)
Total time = \( \frac{d}{80} + \frac{d}{100} = 9 \)
Finding a common denominator:
\( \frac{5d + 4d}{400} = 9 \)
\( \frac{9d}{400} = 9 \)
\( 9d = 3600 \)
\( d = 400 \)
#### 400 kilometers