getting index of character and first instance

Question

need to get the index of character "d" and first instance of character "n"

that what i have attempted so far

using System;

namespace HelloWorld
{
class Program
{
static void Main(string[] args)
{
string greeting = "Good Morning";
int index1, index2;

index1 = greeting['d'];
index2 = greeting['n';


Console.WriteLine(index1 + ", " + index2);
}
}
}