Answer: Nitai is better off working over the weekend.
Explanation:
When Nitai plans to work over the weekend, she gets $125 out of which she pays $15 (i.e $125*0.12) is tax. So, she is left with $125 - $15 = $110 income. If she pays for her repair which costs her $90 she will be left with $110 - $90 = $20.
If she does not work over the weekend, she will have no income and she will have to pay no taxes. Neither will she have money to pay for her car repairs.
So, Nitai is better off working over the weekend as she gets a surplus of $20.