k^3(k7/5)^-5 can be rewritten as (k^3) * (7k/5)^(-5) (must use parentheses around that "-5").
This would be better written as
k^3 k^3 * 5^5
------------ = -------------------
(7k/5)^5 7^5 * k^5
Then k^3 / k^5 reduces to 1 / k^2, and 5^5 / 7^5 reduces to 1 / 5^2, or 1 / 25.
Thus,
the answer in simplest form is
1
-----------
25k^2