Answer:
The test statistic is 1.57.
Explanation:
Our test statistic is:

In which X is the sample mean,
is the value tested at the null hypothesis,
is the standard deviation and n is the size of the sample.
A Seattle department store samples 89 items sold in January and found that 10 of the items were returned.
This means that

7% of all merchandise sold in the United States gets returned.
This means that

For a proportion, the standard deviation is

Test statistic:



The test statistic is 1.57.