The expression 35 + 45x represents a train's distance, in miles, from a terminal after x hours of travel.

How far was the train from the terminal at the beginning of its journey?

This can be represented by the equation d = 35 + 45x, where d is the distance from the terminal and x is hours of travel. At the beginning of the journey the train had travelled 0 hours, so x = 0. Therefore, d = 35 + (45 x 0). D = 35 + 0. The train is 35 miles from the terminal.