Let the total hours that Sam has in a workday be depicted by the letter x.
Sam finds that he spends two-fifths of his work day answering emails which amounts to 3.6 hours.
If we write the above information mathematically, we will get:

We will now isolate x. Thus we have:
hours
Thus Sam has a typical workday of 9 hours. Out of this he spends 3.6 hours writing emails. Therefore, the number of hours Sam worked is:
9-3.6= 5.4 hours.