Nitai should work over the weekend.
Because according to the situation, if he works over the weekend, he will get $500. After deducting the tax, he would still have surplus amount to get his car repaired from the workshop. The offer is profitable, so he should go for the overtime option.
Now how he would have the surplus, following is the calculation
Overtime payment = $500
Tax percentage= 12%
Tax that he has to pay: 500*0.12= $60
Amount earned= $500 - $60= $440
Car Repairing Expense= $400
So, Amount in hand - Expenses = $440 - $400 = $40 (Surplus)
So this this the amount, he would still have in hand, if he works on the weekend.