Final answer:
A straight horizontal line on a rate-time graph best represents Brandon's constant typing speed of 75 words every 45 minutes, indicating a zero rate of change.
Step-by-step explanation:
Graph Representing the Rate of Change in Typing Speed
The graph that best represents the rate of change in Brandon's typing speed, given that he types 75 words every 45 minutes, would be a straight horizontal line on a rate-time graph. Since Brandon is typing at a constant rate, the rate of change is zero and the graph depicting his typing rate would not slope upwards or downwards. Therefore, the graph would show that the typing speed remains the same throughout the 45 minutes. For example, in a graph where time is on the x-axis and typing speed is on the y-axis, the line would be at the height that represents 75 words per 45 minutes (or 1 and 2/3 words per minute), extending horizontally across the graph.