3 Parts with a picture. Thanks!

We have $8.50 an hour gross minus $2.15 an hour tax and bennys.  Then $3.75 daily expense.  In one week our net take-away y after x hours is

y = x(8.50 - 2.15) - 5(3.75)

That's the answer, or we can simplify it to

y = 6.35 x - 18.75

The slope, 6.35, is the net dollars per hour before weekly expenses.

The y intercept, -18.75, is the weekly expense, negative because it's an expense.

To make $120 in a week, we solve for x where y=120

120 = 6.35x - 18.75

138.75 = 6.35 x

x = 138.75 / 6.35 = 21.8503937007874

That wasn't the nice round number I was expecting/hoping for.  I don't see a mistake so let's go with

21.85 hours to make $120