Use the "charges" particles model to show that

9+(-5)=4

x x x x x

x x x x

-x -x -x
-x -x

Now put them in the same group.

x x x x x
x x x x
-x -x -x
-x -x

How many more x's do you have than minus x's?

Please go back and study the site I posted for you.