Answer:
[tex]f(x) = - 2x - 3[/tex]
when x is r + 2 :
[tex]f(r + 2) = - 2(r + 2) - 3 \\ = - 2r - 4 - 3 \\ = - 2r - 7 \\ \\ { \boxed{ \boxed{f(r + 2) = - 2r - 7}}}[/tex]
