Answer:
The standard deviation of the sample is 0.0064.
Step-by-step explanation:
The standard deviation of a sample of length n of a population with standard deviation
is given by the following formula:

In this problem, we have that:
61 randomly selected gas stations. This means that 
The standard error of the mean is $0.05. This means that
.
What is the standard deviation of the sample?

The standard deviation of the sample is 0.0064.