How do I make finite derivatives divided forward, backward and centered in Excel? Need Help

the answer is; biodiversity resulting from few ancestors

adaptive radiation occurs when a population is subjected to a large natural environment with spatial ecological variations. the parts of the population in the different ecologies begin to adapt to their local environments. due to non-random mating across the large populations, this causes the different populations from the large population to speciate within their local environments. they, therefore, diverge to different species sharing a common ancestor.  

the formula of a slope:

we have the points (-2, 7) and (2, 3). substitute:

y-3=-3/2(x+4)

ur very much welcome