To calculate the number of Kanbans needed:
Number of Kanbans = (Usage * (Lead time + Safety stock)) / Container size
Given:
a. Container size = 840
b. Lead time = 3 days
c. Usage = 900 per day
d. Safety stock = 60
Number of Kanbans = (900 * (3 + 60)) / 840
Number of Kanbans ≈ (900 * 63) / 840
Number of Kanbans ≈ 56700 / 840
Number of Kanbans ≈ 67.5
Since we can't have a fraction of a Kanban, the company would need 68 Kanbans to ensure they don't run out of product.