To solve this question, the user needs to compare the distances and costs of each route from City A to City C. Then, evaluate the options given based on the distance and toll.
a) Directly on toll-free highway to City C: This option is not applicable as it does not start from City A.
b) The bridge: The distance is 20 miles and the toll is $0.75. Hence, the total cost would be $0.75.
c) The bridge only if traffic is heavy on the toll-free highway: There is no mention of traffic conditions on the toll-free highway. Hence, this option cannot be evaluated.
d) The bridge or the tunnel: The distance through the tunnel is 10 miles and the toll is $1.00 for the driver and vehicle and $0.10 for each passenger. The total cost depends on the number of passengers. However, the distance through the bridge is 20 miles and the toll is $0.75. Hence, the total cost would be the same as option b) if there are no passengers.
Therefore, the shortest and cheapest route from City A to City C is the bridge, which is option b).
The Answer is: B