To find the total number of cars, \( T \), that have passed through the toll booth \( h \) hours after 8 a.m., we consider the number of cars that pass each hour and the initial number of cars that have already passed by 8 a.m.
- Initial Cars at 8 a.m.: 75 cars have already passed through by 8 a.m.
- Cars Passing per Hour: On average, 45 cars pass through each hour.
So, after \( h \) hours, the total number of cars that have passed through is the initial 75 cars plus 45 cars for each of the \( h \) hours.
The equation representing this situation is:
\[ T = 75 + 45h \]
This equation can also be rewritten as:
\[ T = 45h + 75 \]
Hence, the correct answer is:
A. \( T = 45h + 75 \)