Testing: $H 0: u \geq 13.9$ H1:u<13.9 Suppose you mistakenly failed to reject the null hypothesis in this problem, what type of error is that ?y

Step 1 ：We are testing the following hypotheses: Null Hypothesis (H0): \(u \geq 13.9\) and Alternative Hypothesis (H1): \(u<13.9\).

Step 2 ：If we fail to reject the null hypothesis when we should have rejected it, this is a type of error.

Step 3 ：The type of error that occurs in this case is a \(\boxed{\text{Type II error}}\).