Question 1043491
let t=number of hours
9t is one scale
320+(40-t)3 is the other scale.
For the job equaling 40 hours, the hourly rate is better, so at 40 hours, they make 40*$9 or $360.
9t>320+(40-t)3
9t>320+120-3t
12t>440
t>36 2/3 hours  ANSWER

At 36 hours, they make 36*$9=$324 hourly and $320+$12+$332 by the faster system.
but at 37 hours, they make 37*$9=$333 hourly and $320+$9+$329 by the faster system.