From previous studies, it is concluded that $12 \%$ of workers indicate that they are satisfied with their job. A researcher claims it has decreased and decides to survey 100 adults. Test the researcher's claim at the $a=0.05$ significance level. After surveying 100 adult Americans, the researcher finds that 57 workers indicate that they are satisfied with theil job. Compute the test statistic. Round to two decimal places.

Step 1 ：Given that the sample proportion (\(\hat{p}\)) is 0.57, the hypothesized population proportion (\(p_0\)) is 0.12, and the sample size (\(n\)) is 100.

Step 2 ：The test statistic for a hypothesis test about a proportion is calculated using the formula: \[Z = \frac{\hat{p} - p_0}{\sqrt{\frac{p_0(1-p_0)}{n}}}\]

Step 3 ：Substitute the given values into the formula: \[Z = \frac{0.57 - 0.12}{\sqrt{\frac{0.12(1-0.12)}{100}}}\]

Step 4 ：Solve the equation to find the test statistic.

Step 5 ：The test statistic is approximately 13.85.

Step 6 ：Final Answer: \(\boxed{13.85}\)