Inventory days

Crag Co has sales of $200m per year and the gross profit margin is 40%. Finished goods inventory days vary throughout the year within the following range:

Maximum Minimum
Inventory days 120 90
All purchases and sales are made on a cash basis and no inventory of raw materials or work in progress is carried.

Crag Co intends to finance permanent current assets with equity and fluctuating current assets with its overdraft.

In relation to finished goods inventory and assuming a 360-day year, how much finance will be needed from the overdraft?

I got lost in my attempt to solve this question but the examiner has calculated it like this. $200m x 30/360 x 0.6 = $10m. I have no idea whats going on here. Can you pls explain the steps that I need to incorporate while solving a question like this.