How can a referece to integer constant change value in a function?

[C++ Programming]

Could someone pls explain the below question?

Q1 : In line1 the second parameter is referece to integer constant.

If so how is the value in 'x' changed to 4

Question:

#include

#include

using namespace std;

int mani(int (&arr)[10], const int& x)//Line1
{
for (int i = 0; i < 1; ++i)
arr[i] = arr[i] + x;
return x; //returns 4
}

int main(){
int arr[10] = {2, 3, 4, 5, 6, 7, 8, 9, 10, 11};
cout