Answer: The slope of a line on a distance-time graph is- speed of the object.
The slope of a line on a graph refers to rate of change of variable that is presented on Y axis with respect to the variable that is presented on X axis.
For a distance time graph, distance is presented on Y axis and time on the X axis.
As we know that

Therefore, the slope of a line on a distance-time graph represents speed of the object.