i will mark how is speed shown on a distance-time graph? as the xvalue at the beginning of the lineas the slope of the lineas the xvalue at the end of the lineas the length of the line

as the slope of the line

Explanation:

As we know that the speed is defined as the rate of distance moved by the object.

Here let say that total distance that is moved by the object is "d" and total time taken by the object is "t"

so here average speed is given as

now we say that for small interval of time or for an instant of time the speed is given as

so here it shows that it is slope of distance time graph so speed is the slope of the graph at given point

answer: a) y=-8x+5

a) m= -8

b) m= -2

c) m= 7

d) m= 6