From the question
Initial mile marker = 6, Final mile marker = 13
Initial elevation = 6220ft, Final elevation = 8390ft
The average rate of change in elevation is
[tex]\begin{gathered} \text{change in elevation = }\frac{Final\text{ elevation - initial elevation}}{Final\text{ mile marker - initial mile marker}} \\ \text{Change in elevation = }\frac{8390ft\text{ - 6220ft}}{13\text{milemarker - 6 milemarker}} \\ \text{Change in elevation = }\frac{2170ft}{7mile\text{ marker}} \\ \text{Change in elevation = 310 fe}et\text{ per mile marker} \end{gathered}[/tex]Therefore,
The rate of change in elevation of Randy's position from mile marker 6 to mile marker 13 is 310 feet per mile marker