You should deploy a virtual machine scale set across two availability zones and deploy a load balancer to meet the requirements. An Azure availability zone is a physically separated location within an Azure region. Azure regions contain at least three availability zones (data centers) with their own infrastructure per availability zone (power, cooling, etc.), and are connected with a high performance network. Because the Enterprise resource planning (ERP) web application cannot be modified, it should be deployed on an Azure virtual machine. You should deploy a virtual machine scale set to scale a web application on virtual machines across availability zones with minimized administrative effort. In this scenario, the requirement is met by deploying an ERP web application to multiple availability zones within an Azure region.
You should also deploy an Azure load balancer to route traffic automatically to the failover availability zone.
You should not deploy a web app across two regions. Since CompanyA operates only in East US and there is no interregional availability required, deploying a web app across two regions is not necessary. Deploying a web app across multiple regions also increases costs for the interregional data transfer.
You should not deploy an Azure Traffic Manager profile. Azure Traffic Manager is an Azure load balancing solution to distribute traffic to multiple service endpoints across Azure regions for availability or performance purposes. Since there is no interregional availability required, deploying Azure Traffic Manager is not needed.