A terrain is known to be equally divided between $1,025$ feet above datum, $1,265$ feet above datum, and $1,540$ feet above datum. If the flight elevation above sea level for an aerial photograph is $5,000$ feet and the focal length was $4$ inches, what is the average photo scale?

a$)\frac{1}{750}$

b$)\frac{1}{800}$

c$)\frac{1}{600}$

d$)\frac{1}{550}$

e$)\frac{1}{500}$