Explanation:
Box 1: add a subnet
Your IaaS virtual machines (VMs) and PaaS role instances in a virtual network automatically receive a private IP address from a range that you specify, based on the subnet they are connected to. We need to add the 192.168.1.0/24 subnet.
Box 2: add a network interface
The 10.2.1.0/24 network exists. We need to add a network interface.
References: https://docs.microsoft.com/en-us/azure/virtual-network/virtual-networks-static-private-ip-arm-pportal