You have function [tex]g(x)=x^2- \frac{5}{3} x[/tex]. To count [tex]g(n-7)[/tex] you have to substitute [tex]n-7[/tex] instead of x in the expression of g(x):
[tex]g(n-7)=(n-7)^2- \frac{5}{3} (n-7)=n^2-14n+49- \frac{5}{3} n+ \frac{5}{3} \cdot 7=[/tex]
[tex]=n^2+n(-14- \frac{5}{3} )+(49+\frac{35}{3} )=n^2- \frac{47}{3} n+ \frac{182}{3} [/tex].
