Exam 1Y0-440 topic 1 question 3 discussion

Scenario: Based on a discussion between a Citrix Architect and a team of Workspacelab members, the MPX Logical layout for Workspacelab has been created across three (3) sites.
The requirements captured during the design discussion held for a NetScaler design project are as follows:
Two (2) pairs of NetScaler MPX appliances deployed in the DMZ and internal network.
High Availability will be accessible for each NetScaler MPX
The external NetScaler MPX appliance will be deployed in multi-arm mode.
The internal NetScaler MPX will be deployed in single-arm mode wherein it will be connected to Cisco ACI Fabric.
All three (3) Workspacelab sites: Dc, NDR and DR, will have similar NetScaler configurations and design.
How many NetScaler MPX appliances should the architect deploy at each site to meet the design requirements above?