Question from the Terraform : certification training test

In the following code :

variable "vpc_cidrs" {
  type = map
  default = {
    us-east-1 = "10.0.0.0/16"
    us-east-2 = "10.1.0.0/16"
    us-west-1 = "10.2.0.0/16"
    us-west-2 = "10.3.0.0/16"
  }
}

resource "aws_vpc" "shared" {
  cidr_block = _____________
}

How to define the cidr_block for the region us-east-1 in the aws_vpc.shared resource, using the vpc_cidrs variable ?