rate - rate * tax rate = net rate

8 - 8*0.15 = 6.8

So, est. net at 6.50/hour.
Each 5 hours = $32.50.

10 = $65.00
15 = $97.50
20 = $130.00

--------------------------------
9 - 9*0.15=7.65

5    = $38.25
10  = $76.50
15  = $114.75
20  = $153.00