Okay, here we have this:
Considering the provided information we obtain the following:
Mean of the five week period=((Mean of the past four weeks*4)+Hours worked this week)/5
Replacing:
Mean of the five week period=((35.75*4)+37)/5
Mean of the five week period=(143+37)/5
Mean of the five week period=180/5
Mean of the five week period=36
Finally we obtain that the five week mean is 36 hours.