Final answer:
The term zero on a number line represents the origin, which is between -1.5 and 1.6, in Benjamin's plotted points. It's the central point that doesn't lean toward either negative or positive values, and in graphing context, a horizontal line with a slope of zero also represents no change between x and y values.
Step-by-step explanation:
When Benjamin plotted -1.5 and 1.6 on a number line, he placed two points that correspond to negative and positive values, respectively. The term zero on a number line refers to the origin, which is the central point between negative and positive values. In his scenario, the point for zero would be located to the left of 1.6 and to the right of -1.5. This falls precisely at the central point that separates the negative and positive halves of the number line.
A horizontal line on a graph that has a slope of zero indicates that there is no change in the y-values regardless of the x-values; hence the line remains flat and straight. This concept is different from placing points on a number line but is related to the understanding of how zero functions within a coordinate system.