Your company has the divisions shown in the following table.

Box 1: 2

One management group for East, and one for West.

When creating a blueprint definition, you'll define where the blueprint is saved. Blueprints can be saved to a management group or subscription that you have Contributor access to. If the location is a management group, the blueprint is available to assign to any child subscription of that management group.

Box 2: 2

Box 3: 4

One assignment for each subscription.

"Assigning a blueprint definition to a management group means the assignment object exists at the management group. The deployment of artifacts still targets a subscription. To perform a management group assignment, the Create Or Update REST API must be used and the request body must include a value for properties.scope to define the target subscription." https://docs.microsoft.com/en-us/azure/governance/blueprints/overview#blueprint-assignment