Answer
The probability is:
P(4 calls) = $\frac{17}{20}.\frac{17}{20}\frac{17}{20}.\frac{17}{20}=\frac{83521}{160000}\approx 52.2 %$
Work Step by Step
The events are independents because calling one person does not affect the probability of the other person not taking the survey.
So, write the percent as a fraction which will be the probability:
$85 %$ =$ \frac{85}{100}= \frac{17}{20}$
The probability is:
P(4 calls) = $\frac{17}{20}.\frac{17}{20}\frac{17}{20}.\frac{17}{20}=\frac{83521}{160000}\approx 52.2 %$
