Answer
See the answer below.
Work Step by Step
The slow step is rate-determining so:
$r=k_S[O_3][O]$
we need to eliminate the intermediary; the back fast reaction has the rate:
$r_{-F}=k_{-F}[O_2][O]$
since it's an equilibrium
$r_{-F}=r_F=k_{F}[O_3]$ and $K_F=k_F/k_{-F}$
$r=k_S[O_3]\dfrac{r_F}{k_{-F}[O_2]}=(K_Fk_S)[O_3]^2/[O_2]$
