Answer:
 
    
If we compare the p value and a significance level for example  we see that
 we see that  so we can conclude that we have enough evidence to FAIL to reject the null hypothesis, so we can conclude that the true mean it's not significantly less than 20 min.
 so we can conclude that we have enough evidence to FAIL to reject the null hypothesis, so we can conclude that the true mean it's not significantly less than 20 min.
Step-by-step explanation:
Data given and notation    
 represent the average lateral recumbency for the sample
 represent the average lateral recumbency for the sample    
 represent the sample standard deviation
 represent the sample standard deviation    
 sample size
 sample size    
 represent the value that we want to test
 represent the value that we want to test    
 represent the significance level for the hypothesis test.
 represent the significance level for the hypothesis test.    
t would represent the statistic (variable of interest)    
 represent the p value for the test (variable of interest)
 represent the p value for the test (variable of interest)    
State the null and alternative hypotheses.    
We need to apply a left tailed  test.  
What are H0 and Ha for this study?    
Null hypothesis:   
  
Alternative hypothesis : 
  
Compute the test statistic  
The statistic for this case is given by:  
 (1)
 (1)    
t-test: "Is used to compare group means. Is one of the most common tests and is used to determine if the mean is (higher, less or not equal) to an specified value".    
Calculate the statistic    
We can replace in formula (1) the info given like this:    

The degrees of freedom are given by:
 
    
Give the appropriate conclusion for the test  
Since is a one side left tailed test the p value would be:    
 
    
Conclusion    
If we compare the p value and a significance level for example  we see that
 we see that  so we can conclude that we have enough evidence to FAIL to reject the null hypothesis, so we can conclude that the true mean it's not significantly less than 20 min.
 so we can conclude that we have enough evidence to FAIL to reject the null hypothesis, so we can conclude that the true mean it's not significantly less than 20 min.