What does this C++ snippet output?

1#include <iostream>
2 
3struct Shape {
4  virtual double area() = 0;
5  double describe() { return area() * 2; }
6};
7struct Box : Shape {
8  double area() override { return 5; }
9};
10int main() {
11    Box b;
12    std::cout << b.describe() << "\n";
13}