What is x, y and z? show your work

x - y + 9z = -27

2x - 4y - z = -1

3x + 6y - 3z = 27

Darcy deposited $390 into a savings account. as long as the account balance remains at or above $150, she does not have to pay a service fee for the account. for how many months can she withdraw $40 a month without having to pay service fees? a) 3 b) 5 c) 6 d) 9