Answer
$P(Excellent~|~C)=\frac{13}{30}\approx0.433$
Work Step by Step
$N(C)=6+11+13=30$ and $N(C~and~Excellent)=13$. Using the Conditional Rule (page 288):
$P(Excellent~|~C)=\frac{N(C~and~Excellent)}{N(C)}=\frac{13}{30}\approx0.433$
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