D. 12.5
The equation to find the average rate of change is
[tex] \frac{y2 - y1 }{x2 - x1} [/tex]
To find the average rate of change between points (0,20) and (8,120) you need to plug it into the equation so it'll be
[tex] \frac{120 - 20}{8 - 0} [/tex]
this simplifies to
[tex] \frac{100}{8} [/tex]
which is 12.5
