Simple,
6 hours Monday through Friday....
That's 5 days...thus..
6*5=30
Now, the employee also has 3.5 hours Saturday morning, so..
30+3.5=33.5
This employee, though, wants to work 40 hours. The employee has 30.5 so far, to find the rest...
40-33.5=6.5
Thus, the employee needs to work an additional 6.5 hours (h).