We know profit from the equation below:

Revenue - Cost = Profit

We're given Profit as 42, so we have:

Revenue - Cost = 42

Let hours worked be h. We have revenue as:

Revenue = 8h

Cost = 40, so we plug these into profit to get:

8h - 40 = 42

To solve this equation for h, we plug this equation into our math engine and get:

h =

**10.25**