Net pay is calculated by subtracting deductions from Net Pay.
In this case:
Gross Pay is 40 hours X $9/hr (regular pay) PLUS 3 hours X (13.50 -- 1.5 times the normal pay) for overtime
Once you have Gross Pay, you multiply that by the percentages given for the deductions and subtract that total from Gross Pay.
One note, in this case, federal taxes are not withheld from the amount given to 401(k). So to figure the taxes you would:
(Gross Pay - 401(K) contribution) X 10%
Gross Pay - deductions = net pay