Answer
$0.3125$
Work Step by Step
We are interested in the event $(E)$ that an established author is successful.
The sample size is $N=80$, (There are 80 established authors)
The frequency of $E$ is $fr(E)=25$ (There are 25 successful established authors)
The relative frequency of $E$ is $P(E)=\frac{fr(E)}{N}=\frac{25}{80}=0.3125$