Nothing would be printed.
Your code wouldn't even compile.
for (int i=20; i>0; i = i-2)
{
Console.WriteLine(i)
}
A semicolon is missing at the end of line 3.
If you corrected this error like this:
for (int i=20; i>0; i = i-2)
{
Console.WriteLine(i);
}
then you would get the result as described in solution 1.