5^2(n+6)*25^2n-7/125^2n
You might want to add some parentheses or more carefully write out the problem.
Do you mean (5^2)(n+6) * (25^2)(n-7) / ( (125^2)n ) ?
Do you mean 5^(2n+6) * 25^(2n-7) / (125^(2n)) ?
Do you mean (5^2)(n+6) * (25^2)n - ( 7 / (125^(2n) ) ?
. . . etc., etc.. ?