Answer
$P(\text{Maxfli or Top-Flite})=0.55$
Work Step by Step
$N(Titleist)=9$, $N(Maxfli)=8$ and $N(Top-Flite)=3$
Let S be the sample space. $N(S)=N(Titleist)+N(Maxfli)+N(Top-Flite)=9+8+3=20$
$P(Maxfli)=\frac{N(Maxfli)}{N(S)}=\frac{8}{20}=0.40$
$P(Top-Flite)=\frac{N(Top-Flite)}{N(S)}=\frac{3}{20}=0.15$
The events "Titleist" and "Maxfli" are mutually exclusive, so:
$P(\text{Maxfli or Top-Flite})=P(Maxfli)+P(Top-Flite)=0.40+0.15=0.55$