Why does m[1] - m[0] return 3 where m is a 3x3 matrix?

This is my code:

int m[][3] = {
               { 0 , 1 , 2  },
               { 10, 11, 12 },
               { 20, 21, 22 }
             };
printf("%d %d\n", m[1] - m[0], m[1][0] - m[0][0]);

And why does

m[1] - m[0]

return 3? I know why the second expression would return 10 but the 1^st one doesn't seem logical to me.