Jack needs workers to clean his driveway for the current season. Each

Jack needs workers to clean his driveway for the current season. Each worker costs $4000/month. The current season has 5 months, and Jack is willing to hire 150 workers per season. What will be the cost per season incurred by Jack?

A $600K
B $120K
C $300K
D $200K
E $100K



Source - GMAT Book by Kaplan/Princeton (I forgot)

I am not sure how I can represent current wage -- is it $4000/month/person or $4000/person/month or $4000/(person * month). Here's why:

Case (i) Wage = $4000/month/person

150 people are hired in one season, and there are 5 months in one season.

Therefore #of months/person = 5 month/season * 1 season/150 person = 1 month / 30 person.

Therefore, total cost = $4000/(month/person) * 1 month / 30 person = $4000/30 (What will be the unit? I believe "$")

Case (ii) Wage = $4000/(month*person)
Therefore total cost =$4000/(month*person) * 5 months/ season * 150 people / season = $4000*5*150 / season = $3000K / season (what will be the unit? 1/season^2?)

Case (iii) Wage = $4000/person/month
Therefore total cost = $4000 / person / month * (150 person / season) * (1 season/month) = $120K (units = $/(month)^2?? or $/month?) I really confused. Therefore, total cost per season = $120K * 5 = $600K

I am not sure which case is correct/incorrect and why. I would appreciate any help.

Thanks