Answer
$.786$
Work Step by Step
We are interested in the event $(E)$ that an unsuccessful author is established.
The sample size is $N=70$, (There are 70 unsuccessful authors)
The frequency of $E$ is $fr(E)=55$ (There are 55 unsuccessful established authors)
The relative frequency of $E$ is $P(E)=\frac{fr(E)}{N}=\frac{55}{70}\approx .786$