+ operator

Question

Could you explain me please how does it works:
int x =9;
x+=++x;
Console.Write (x);

Answer 1

While it may be OK for challenge questions etc. in your own code try to avoid writing statements like: x+=++x

Answer 2

X += ++X; means
X = X + ++X;
X = (9+1) + (1+9);
X= 20

Answer 3

x+=++x means x plus x+1= 9+10=19?