How did most Americans used to know when it was “noon” before the railroads were completed?

The need for continental time zones stemmed directly from the problems of moving passengers and freight over the thousands of miles of rail line that covered North America by the 1880s. Since human beings had first begun keeping track of time, they set their clocks to the local movement of the sun. Even as late as the 1880s, most towns in the U.S. had their own local time, generally based on “high noon,” or the time when the sun was at its highest point in the sky. As railroads began to shrink the travel time between cities from days or months to mere hours, however, these local times became a scheduling nightmare. Railroad timetables in major cities listed dozens of different arrival and departure times for the same train, each linked to a different local time zone.

the answer is b. 300t + 3/2xt